In a large bowl, mix the first 6 dry ingredients for the cake batter. Whisk in the melted butter, half & half, eggs, and vanilla. Pour the batter in the prepared baking dish and bake for 22-25 minutes, until a toothpick inserted into the center of the cake comes out clean. Cool completely before proceeding. *Do not open the oven door before 22 minutes have passed or the cake might collapse.
Once the cake is cool, prepare the mint filling. Place all ingredients in a microwave-safe bowl and microwave on high for 2 minutes. Stir vigorously to melt the chips. Microwave one more minute and whisk until smooth, if needed. Pour the mint layer over the surface of the cake and smooth out evenly. Place the cake in the refrigerator to set the mint filling.
Once the mint filling is dry to the touch make the chocolate glaze. (It doesn't have to be firm, just dry.) In a medium bowl, whisk the melted butter, cocoa powder, half & half, and vanilla together. Once smooth, whisk in the powdered sugar. The mixture should be loose and spreadable. Pour over the cake and spread evenly. Allow the cake to rest for at least an hour, so the glaze has time to set. Cut and serve at room temperature.
If you prefer a traditional fluffy frosting, follow the chocolate glaze recipe, but use softened butter, not melted. Beat the butter in a mixer then add the cocoa and 3 tablespoons half & half and vanilla extract. Beat in the powdered sugar and spread over the cake.