Preheat oven to 350F. Spray a quarter sheet pan with baking spray.
Prep your frosting ingredients and have ready for later.
Prepare your cake mix according to the box instructions. Turn the batter out into the prepared pan and spread out evenly with an offset spatula. Bake for 20 minutes, or until the cake springs back when gently touched, and the edges are just beginning to turn golden. A toothpick inserted near the center should come out without wet batter on it.
While the cake bakes, prep your frosting. Put the butter, cut in chunks, and the half and half in a medium saucepan and heat to melt the butter. Set aside.
Once the cake comes out of the oven, place it on a cooling rack and bring your frosting mixture to a simmer. Add the sugar and almond extract and whisk or stir with a silicone spoonula until the frosting is smooth and pourable, but not too thin or too thick. Add extra sugar if you need to thicken it. Stir the almonds into the frosting and immediately pour over the warm cake, spreading the frosting out with an offset spatula.
Your cake can be kept at room temperature for 2 days. It may also be refrigerated.
Notes
*The correct way to measure a pan is from outer edge to outer edge.