This from-scratch tres leches cake is a butter-less sponge soaked overnight in evaporated milk, sweetened condensed milk, and half-and-half, then topped with whipped cream. Make it a day ahead — it only gets better.
Whisk together flour, cornstarch, salt, and baking powder.
With an electric mixer or a stand mixer with a whisk attachment, beat egg whites on medium speed until soft peaks form. They'll be foamy first, but will stay somewhat upright on the beater when they're soft peaks.
Gradually add 1 ¼ cups sugar, a few tablespoons at a time, and beat on medium speed until stiff peaks form. The mixture will become shiny, and the peaks will stay upright, without bending over. Slow the mixer down if they're close to stiff peaks but not quite there, as egg whites overwhip quickly.
Still on medium speed, add vanilla extract and egg yolks, one at a time. Switch to low speed, and add milk just to combine.
Using a rubber spatula, fold in the flour mixture in one-third at a time. To fold, insert a rubber spatula down the middle to the bottom of the bowl, then scrape up along a side to "fold" the batter over.
Scrape batter into a greased 9x13-inch pan, and smooth it out. Bake at 350F for 25-35 minutes, until top is lightly browned and until a toothpick inserted into the center comes out clean. (If the cake jiggles when you touch the pan, let it bake longer before testing it.)
Let the cake cool completely before soaking with milk.
Soaking
In 4-cup measuring cup or a large bowl, whisk together evaporated milk, sweetened condensed milk, and 1 ½ cup half-and-half. Set aside ½ cup of the mixture for serving.
Use a fork or toothpick to poke holes all over the cake. Pour all the milk mixture, except for the ½ cup you've reserved, on the cake, up to and including the edges. Cover and refrigerate at least 4 hours.
Topping and Serving
Immediately before serving, whip 1 ½ cups heavy cream and 1 tablespoon sugar until soft peaks form. Spread the whipped cream on top of cake.
Serve cake right after topping, garnishing with a little of the milk mixture if desired.
Immediately store remaining cake in the fridge. Leftovers are good up to 4 days later; whipped cream deflates somewhat, but it doesn't affect the flavor or texture of the cake.
Notes
Flour plus cornstarch equals cake flour. You can substitute flour for the cornstarch if necessary. You also can substitute cake flour for the flour and cornstarch.Evaporated milk and sweetened condensed milk are not interchangeable. You may use cream in place of the half-and-half. Err on the side of overbaking the cake rather than underbaking it so it fully absorbs all the milk. The cake should also completely cool, or else it risks becoming mushy. Dairy absorbs odors and flavors easily, so keep the cake well covered in the refrigerator. Adapted from Smitten Kitchen's recipe. She says to bake 18-24, but my cake consistently takes 28 in a metal pan (in 2 different ovens), and 32 in a glass one. Calorie count is an estimate only.