Place the strawberries and ½ cup (100g) sugar in a high-sided saucepan with a splash of water, over medium heat. For more details on making puree, check out my strawberry puree post.
Heat until the strawberries start to break down and begin boiling. Use a wooden spoon or potato masher to help squish them down. Stir regularly. Keep boiling until a lot of the liquid has evaporated and the mixture looks slightly gelatinous, about the thickness of jam (about 10-15 mins).
Let cool for 10 minutes, then add to a food processor and blitz until completely smooth.
Pass the strawberry puree through a fine mesh sieve to remove any remaining chunks or seeds. (Use a spoon to help push it through the sieve). Let cool completely.
Make the Angel Food Cake
Preheat oven to 350°F / 180°C (or 160°C fan assisted).
Place the room-temperature egg whites and cream of tartar in the bowl of a stand mixer with a whisk attachment fitted and whip on low speed until they are white and frothy.
Gradually turn the mixer up to medium-high speed and start adding the sugar, one tablespoon at a time, letting it whip for about 15 seconds in between each addition. Do this until all the sugar is incorporated and the meringue forms medium-soft peaks. Feel a bit of the meringue between your fingers, it should be smooth - if it is gritty, continue to whip for another couple of minutes.
Add ¾ cup (180g) of the prepared strawberry puree from earlier into the meringue along with the vanilla extract. Save the rest of the puree to spoon over the finished dessert later. Turn the mixer on low speed and gently whisk it in. If you want to add a pop of pink food color to your cake, add it in now. Once the strawberry puree is totally mixed in, turn the mixer back on high speed for 1 minute.
Mix the salt in with the cake flour and sift it twice. Then sift ⅓ of the mixture into the strawberry meringue. Gently fold the flour into the meringue until it is almost completely incorporated. Repeat with half of the remaining flour, then again with the last of the flour and fold it in completely.
Spoon the cake batter into an ungreased tube pan.* Smooth it out and then bake for 35-40 minutes. A skewer inserted into the middle of the cake should come out clean and the top should be golden brown and springy to the touch.
Remove from the oven and immediately turn the pan upside down. If your angel food cake pan has little feet on the bottom, rest it on those. If it doesn't, place the pan upside down over a wire cooling rack. Let it cool completely.
Once the cake is completely cool, use a spatula or knife to run around the edge of the cake pan to help release it, then give the bottom a few taps and the cake should come out.
Egg Whites - If you are in the UK, you only need 10 egg whites. This is because large eggs in the UK are bigger than large eggs in the US. The total amount of egg white needed is 400g. It's better to use fresh eggs than carton egg whites, as the carton ones often don't whip up properly. Don't throw away your egg yolks, keep them for another recipe, like my Custard Cake.
Strawberries - You can use fresh or frozen strawberries for this recipe.
Cream of Tartar - This helps keep the whipped egg whites stable, which is important for baking. If you don't have cream of tartar, you can use a teaspoon of lemon juice instead, but the results won't be quite as good.
*Tube PanIt's very important that your tube pan is ungreased - if you grease it, then the cake won't rise properly, as it needs to cling to the sides of the pan to rise. It is also important to use a tube pan (with a hole in the middle) and not a bundt pan, as it needs the straight sides and bottom in order to rise properly. Serving Tip:Use a serrated knife (like a bread knife) to cut angel food cake, as a regular knife will just squash the slices.