Move over, rainbow bagels—the internet has a new obsession. The latest trend in baking is magic cake, the deceptively simple recipe that uses everyday ingredients to make an otherworldly dessert. As it bakes, the cake batter magically transforms into three layers: a rich, luxurious custard crust, a creamy center, and a light, delicate angel food cake topper.
And though they say magicians shouldn't give away their secrets, there's no real surprise behind the magic here: by whipping egg whites and folding them into the batter, you create an airy but sturdy structure. As the cake bakes, the egg whites expand and the egg yolks settle into a creamy custard.
If you've always been afraid of the folding technique, try it here, and go slow. The cake will still turn out even if all the whites aren't completely incorporated, so don't worry if there are cloud-like pockets of egg white in the batter.
Preheat the oven to 325 degrees F and grease an 8- or 9-inch square metal or glass baking pan.
With an electric hand mixer, beat the egg yolks and sugar together in a large bowl on low speed for about 1 minute, until the yolks and sugar form a pale, thick paste.
Slowly pour in the melted butter and the vanilla extract and mix until incorporated.
Whisk the flour and salt together in a small bowl.
By hand, whisk 1/3 of the flour into the batter until blended, then whisk in 1/3 of the milk. Repeat with the flour and milk until all ingredients are blende
With an electric hand mixer or stand mixer fitted with the whisk attachment, beat the egg whites for about 1 minute on medium-high speed until thick and foamy.
Add the cream of tartar and beat for about 1 minute more until stiff peaks form. (If you don't have a whisk attachment for your hand mixer, clean the beaters and dry very well before using them to beat the eggs; it may take more time to achieve stiff peaks without a whisk.)
Gently and slowly fold the egg whites into the liquid batter with a spatula. An easy technique for folding is to scrape around the edge of the bowl with the spatula, then "fold" the batter into the middle of the bowl on top of itself.
Pour the batter into the greased pan and bake for about 45 minutes to 1 hour. Timing will vary based on your oven and the pan used. The cake is done when it has risen high in the pan with a golden brown top crust, and barely jiggles when you gently shake the pan.
Transfer to a wire rack and cool completely in the pan.
When the cake is cool, make the ganache: Pour the chopped chocolate into a medium bowl. Heat the cream to a simmer, then pour over the chocolate. Let the chocolate and cream rest for 1-2 minutes, then gently stir until the chocolate is completely melted.
Pour the ganache over the cake and gently spread with a spatula until the cake is evenly covered.
Sprinkle with rainbow sprinkles or other decoration as desired.
Refrigerate for at least 2 hours until the ganache has hardened.
Slice and serve.