Preheat your oven to 335°F / 170°C and line two 9-inch baking pans.
Add all the chocolate cake ingredients (except the hot water) into a mixing bowl and mix on low until everything is combined. Make sure to scrape down the sides of the bowl.
2 cups All purpose Flour, 2 cups White Sugar, 2 Large Eggs, ⅔ cup Cocoa Powder, ⅔ cup Vegetable Oil, 1 cup Milk, 2 teaspoon Baking Powder, ½ teaspoon Salt, 1 teaspoon Vanilla
Once the batter is completely combined, add the hot water and mix it in completely.
½ cup Hot Water
Divide the batter evenly between the two cake pans and bake for 25-35 minutes or until a skewer comes out clean.
Make the Strawberry Puree
Place strawberries and sugar in a high-sided saucepan and cook on medium heat. If you are using fresh strawberries, add a splash of water too. Stir occasionally and keep cooking until the strawberries start to break down.
17 oz Strawberries, ½ cup White Sugar
Mash the strawberries a little with a potato masher and continue to cook until the mixture comes to a boil. Keep boiling, stirring occasionally until the mixture thickens slightly and has a kind of gelatenous look to it. (Will take at least 15 minutes from the point of boiling, but could be longer depending on how much liquid was in your strawberries).
Remove from the heat and allow to cool for 15 minutes.
Transfer the strawberry mixture to a food processor or blend with an immersion blender until smooth.
Pass the mixture through a sieve to remove any seeds and then allow to cool completely before using.
Make the Strawberry Italian Meringue Buttercream
Make sure the egg whites and butter are at room temperature before beginning.
Place 1 cup of the sugar into a saucepan along with the water and set aside. Place the remaining ⅓ cup of sugar next to your stand mixer.
1 ⅓ cups White Sugar, ⅓ cup Water
Add the egg whites and cream of tartar to a very clean stand mixer bowl and whip on medium speed until they start to get frothy.
160 g Egg Whites, ½ teaspoon Cream of Tartar
Once they start to froth up, start adding the reserved sugar, one tablespoon at a time, letting it mix in for at least 30 - 60 seconds in between additions. Keep going until all the sugar has been added. The meringue should be thickened to soft peaks by now. Keep it whipping on medium speed while you prepare the sugar syrup.
Place the saucepan with the sugar and water on medium heat, with a thermometer, and bring it to a soft bubble. Do not stir. Once the sugar has all dissolved and the thermometer reads 240°F / 115°C, it's ready to use. Note: If you are confident in the kitchen, you can boil the sugar syrup and mix up the egg whites at the same time, but if this is your first time you may want to do the egg whites first, then the syrup.
With the mixer on low speed, start pouring the sugar syrup into the egg whites in a very slow and steady stream, being careful not to hit the side of the bowl or the whisk. Keep going until it has all been added.
Once the sugar syrup is all into the meringue, the bowl should feel hot to touch. Continue whipping on high until the bowl feels cool.
When the bowl feels completely cool, you can begin adding the butter. The butter must be at room temperature or it won't incorporate properly. Keep whisking the meringue on high speed while adding the butter one small chunk at a time. Let it mix in completely before adding the next tablespoon of butter
3 sticks Butter
About halfway through adding the butter your frosting will be a very strange consistency - don't panic! Just keep adding the butter and it will thicken.
Once all the butter is incorporated, add the vanilla and whip for another minute. You should have a thick, glossy frosting.
1 teaspoon Vanilla
Now add in the cooled strawberry puree a little at a time until you achieve the strength of strawberry flavor you want. If you want a punchier flavor you can add a few drops of strawberry flavor to boost it, but I don't think it needs it.
If you aren't going to use the buttercream right away, store it in the fridge in an airtight container and then let it come back to room temperature and whip it on high again for a minute or two before using.
Assemble the Cake
Once the chocolate cakes have completely cooled, use a cake leveler or serrated knife to cut the domes off the top of the cakes.
Cut each cake layer again about half way down to make 4 thin layers of cake.
Place one layer of chocolate cake on your cake board or serving plate and put some of your strawberry buttercream on top, smoothing it out to an even layer.
Place the next layer of cake on top and spread with more buttercream.
Optional extra: For even more strawberry flavor, you could chop up some fresh strawberries and place them in the middle layer here for a fruity surprise.
Repeat until all layers are on, then cover the whole cake in frosting and smooth out.
Decorate as you like. I chose to do a chocolate ganache drip, buttercream swirls and chocolate covered strawberries. Read the post above for details on how I did this, and inspiration for other decoration ideas.
Notes
If you don't want to make the strawberry puree from scratch, you can use storebought strawberry puree or strawberry jam. Just make sure it's nice and thick and not too liquidy or it may ruin the consistency of your Italian Meringue Buttercream. If it is to runny, try heating it in a saucepan to reduce it a little.