Creme Mousseline

Light, silky and sweet - Creme Mousseline makes a wonderful filling for pastries, desserts and treats.

Chances are you have had creme mousseline before and just don't know it. It is a popular filling in many desserts, but particularly in classic French pastry. It is often used as a rich filling for many popular treats such as Paris brest, eclairs, layer cakes, and profiteroles (cream puffs). I used it recently to make my Fraisier Cake (French Strawberry Cake).

If you love custard-based desserts, you are going to love using creme mousseline as your new favorite filling! You may also enjoy my Perfect Vanilla Custard Cake recipe, or my Custard Donuts. Or take it to another level with baked chocolate custard in my French Chocolate Flan recipe.

Jump to:

• What is Creme Mousseline?
• Ingredients
• Instructions
• How to Get Different Thicknesses for Various Uses
• Storage
• Recipe

What is Creme Mousseline?

Creme mousseline is a delicious custard-based filling used by pastry chefs in many different desserts. It is basically just crème pâtissière (pastry cream / custard) mixed with whipped butter. It creates a beautifully light and silky result that can be used as a filling in classic pastries, as frosting in cakes, or even just eaten as a dessert with a fruit puree. You can make various thicknesses by varying the ratio of pastry cream to butter. It's essentially the same thing as German Buttercream (Custard buttercream), but the process and ratios are a little different, yielding a slightly different consistency and texture.

Ingredients

Egg Yolks - Use large eggs and try to use free-range if you can. We won't need the whole egg for this recipe so just save the egg whites for another bake such as Italian Meringue Buttercream.

Milk - It's important to use whole milk to make the pastry cream as we need the fat content to carry the flavor and consistency.

Sugar - It's best to use white sugar and make sure it is superfine (caster sugar in the UK)

Flour - We'll just use a small amount of flour as a thickening agent in the custard. All-purpose flour is great here.

Corn Starch - Corn starch (cornflour in the UK), is another thickener for the custard.

Vanilla - Make sure you use a high-quality vanilla in the pastry cream as it is a key flavor and will really shine through. Vanilla extract or vanilla bean paste are both great. Or even use a vanilla pod if you have one. Try to avoid vanilla essence.

Butter - Use unsalted butter and make sure it is at room temperature before beginning. I like to remove it from the fridge about an hour before using it. The amount of butter will depend on what you want to use the creme mousseline for. If you want to want it to be a soft filling to go inside choux pastry or something, you want a 2:1 ratio of pastry cream to butter (in terms of weight). If you want the creme mousseline to set hard and firm like in a mousse cake, then use a 1:1 ratio of pastry cream to butter.

See recipe card for quantities.

Instructions

We start by making a regular pastry cream using a classic custard method. Then once it has cooled we will whip the cooked custard into the butter to make the mousseline cream. This is my classic pastry cream recipe I use in all my custard-based desserts.

• Start by taking two tablespoons of the total sugar and putting it into a bowl along with the egg yolks, flour, cornstarch and salt - whisk to combine and then set aside.

• Put the remaining sugar into a saucepan with the milk and vanilla, and slowly warm over medium heat.

• When it begins to get warm, drizzle a small amount of warm milk mixture into the egg yolk mixture and whisk, then add a little more. Keep going until the rest of the milk is together in the bowl with the egg mixture, then pour the whole mixture back into the saucepan. It's important to do this slowly and gradually so you don't scramble the eggs.

• Keep heating the mixture on medium-low heat. whisking constantly until it begins to thicken and boil. Boil for one minute. When it's ready you should be able to coat the back of a spoon and draw a line in it with your finger. Remove from the heat.

• Pass the pastry cream through a fine mesh sieve into a bowl to make sure there are no lumps. At this point, I also like to weigh how much pastry cream was yielded so I know how much butter to add for my desired result (see the section below on making different thicknesses of creme mousseline).

• Cover with plastic wrap (make sure the cling wrap is touching the surface of the pastry cream to prevent a skin forming) and let it cool completely. Don't place it in the fridge, just leave it on the counter let it come to room temperature (about 2 hours). If you are making the pastry cream ahead of time, you can place it in the fridge once it is cool enough, but just make sure you take it out to come to room temperature before again before moving on to the next step. It is essential the pastry cream is not cold when we mix it with the butter or they won't combine properly.

• When the pastry cream is nearly cooled, remove butter from the fridge to come to temperature for about an hour. It should be room temperature but we don't want super soft butter.

• Whip the softened butter on high speed until very pale and creamy. I highly recommend you use a stand mixer with a whisk attachment for this. You could use a handheld electric mixer but it will take a while for the butter to be whipped enough so it could become tiring. I whipped my butter on high speed for about 3 minutes. It should look like slightly yellow whipped cream.

• Turn the mixer speed down to medium speed and add a dollop of pastry cream to the butter. Slowly add the rest of the pastry cream 1 tablespoon at a time, whipping for about 20 seconds in between each addition. It's important to take this slow so the liquid and fat can combine properly. Once all the pastry cream is added, turn the mixer back on high and whip for another minute.

• Your creme mousseline is now ready to use! It should have the consistency of a stable cream and should be firm enough to pipe or spread on a cake. If it is not firm enough, whip for another minute or two until it thickens. If it still isn't thick enough or if it looks curdled, it may be a temperature problem, If you started with cold pastry cream, try letting everything sit out for a little longer then attempt whipping again. If the mixture seems too warm and gloopy, place it in the fridge for 15 minutes and try again.

How to Get Different Thicknesses for Various Uses

Creme mousseline is incredibly versatile, you can tweak the ratios of pastry cream to butter to make for different consistencies to be used in different ways. If you want a soft and smooth creme mousseline, almost like pudding that can be used as a pastry or tart filling, you should use a ratio of 2:1 - 2 parts pastry cream to 1 part butter. If you want the creme mousseline to set firm like a mousse cake that you can slice and have it hold its shape, as in my Fraisier Cake recipe, use a ratio of 1:1.

To do this, weigh the amount of pastry cream that you are left with after you pass it through a sieve, then calculate how much butter to use accordingly.

For example, if I weigh my cooked pastry cream and have 500g of it, I would use the following:

For a thick consistency that will set firm - 500g butter

For a softer, more fluid consistency, like pudding - 250g butter.

The quantities in the recipe card below are to make the firmer creme mousseline, as for moulded desserts But if you are looking for the softer then only use half of the butter in the recipe.

Note: If you are using the thicker consistency to make a moulded dessert, you need to use the creme mousseline as soon as it is ready and then put it in the fridge to set. If you put it in the fridge first it will set and it will be near impossible to pipe or get into any kind of mould or cake pan.

If you are using the softer consistency, you can store it in the fridge until you are ready to use as it will remain soft and pipeable.

Storage

Creme mousseline needs to be kept in the fridge as it is dairy-based. If you use it in a dessert, the whole dessert should be stored in the fridge. If you are using it as a filling in a pastry or dessert, I recommend storing the creme mousseline in the fridge in an airtight container until you are ready to serve, that way your pastry will not get soggy from the moisture in the creme mousseline. You can store the creme mousseline in the fridge for up to 5 days.

Recipe