Preheat the oven to 350 degrees. Lightly grease the bottom of a 9×13 baking pan.
Sift the gluten free all purpose flour with the cocoa, xanthan gum, baking powder, baking soda and salt together in a medium bowl; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, add the butter and beat until creamy.
Slowly add the brown sugar and the granulated sugar to the butter and whip until fluffy.
Add the eggs and the egg yolks one at a time, then add the vanilla.
Turn the mixer to low and alternately add the flour mixture and the buttermilk.
Pour the batter into the prepared pan and bake in the preheated oven for 30-35 minutes until the cake is springy to the touch. Set aside to cool while you prepare the 'tres leches':
For the Glaze:
1 (12-ounce) can evaporated milk
1 (14-ounce) can sweetened condensed milk
1 cup half-and-half
Whisk together the evaporated milk, sweetened condensed milk and the half-and-half in a 1-quart measuring cup. Once combined, pour the glaze over the cake. Refrigerate the cake overnight.
For the Topping:
2 cups heavy cream
8 ounces sugar
1 teaspoon vanilla extract
maraschino cherries, for garnish (optional)
Place the heavy cream, sugar and vanilla into the bowl of a stand mixer. Using the whisk attachment, whisk together on low until stiff peaks are formed. Change to medium speed and whisk until thick. Spread the topping over the cake and allow to chill in the refrigerator until ready to serve.