Strawberry Filled Angel Food Cake is undeniably the perfect summer dessert. An airy, delicately sweet angel food loaf cake is filled to the brim with a fresh strawberry filling and is frosted with irresistible whipped cream! This small-batch cake is made without gelatin, too, so it's vegetarian-friendly!
Preheat oven to 350°F. Line an 8.5x4.5 inch loaf pan with foil (if it's a non-stick pan). This ensures the cake will rise in the pan as the foil helps it"crawl" up.
In a medium mixing bowl, stir together flour, cornstarch, and half of the sugar. It's ok to eyeball half of the sugar; otherwise, measure out 6 tablespoons (which is half of 3/4 cup).
Using a stand mixer with the whisk attachment or a hand-held mixer, beat egg whites, cream of tartar, both the vanilla and almond extracts, and salt. Beat on medium speed until soft peaks form, about 1 minute. Slowly add the remaining sugar and beat on high for approximately 2 more minutes until stiff peaks form. Be careful to not over-mix here, just beat until stiff peaks form.
Add the flour mixture into the egg whites in batches, folding it in completely until no lumps remain. This may take up to 5 minutes to fully combine the two. Spread the batter evenly in the prepared loaf pan.
Bake the cake for 32-36 minutes until the top is golden brown and is not sticky to the touch. You can also use a toothpick and make sure it comes out clean.
Once the cake is baked through, place it, still in the pan, upside down with the edge of the loaf pan resting on top of two cans. Let the cake cool completely for approximately 1 hour.
As the cake cools, combine the strawberries and sugar in a medium mixing bowl. Let the berries sit for 30 minutes. Drain the liquid off of the strawberries. You should have approximately 1/4 cup juice. Add water until you have 1/2 cup liquid total. It's ok if you have more strawberry juice, just add less water to make 1/2 cup.
Add the strawberry juice mixture to a medium saucepan and bring to a boil. Add the agar-agar flakes and whisk until dissolved. Continue to boil for 10 minutes, whisking occasionally.
Remove from heat and stir in the strawberries, slightly mashing them as desired. Set the mixture aside to cool and thicken for 20-30 minutes.
In a chilled mixing bowl, use a standing mixer with a whisk attachment or an electric hand mixer, add heavy cream and powdered sugar. Beat until soft peaks form, approximately 3-5 minutes. Store in fridge if not using immediately.
Once the cake is completely cooled, remove it from the loaf pan. Use a serrated knife to cut off 1/4 of the cake top, approximately 1-2 inches. Set the top aside.
In the base of the cake, use the serrated knife to cut a rectangle in the center, leaving approximately an inch and a half of an edge around the cake. Cut the knife about an inch deep or so, because you will pull out the rest of the center.
Use your hands to scoop out the center of the rectangle, creating space for the filling. Don't go all the way to the bottom of the cake, but leave approximately 1 inch at the bottom.
Pour the strawberry mixture into the rectangle center. Spread whipped cream along the exposed edges of the cake, then add the top back on, using the whipped cream to adhere it. Then, frost the exterior of the cake with the remaining whipped cream. Let the cake set in the fridge for 15-20 minutes, then garnish as desired right before serving. Use a serrated knife to cut for the best results.