Cream butter and sugars together in mixer bowl for 3 minutes
Add mayonnaise, half and half, and vanilla extract, mix to incorporate
Add eggs one at a time, fully incorporating each egg before adding the next
In a separate bowl, mix flour, baking powder, and salt
Add dry ingredients to wet ingredients in two batches, mixing between additions
Grease a 9x13 casserole dish or grease and flour a Bundt pan
Pour batter into prepared pan and smooth into an even layer
Bake in preheated 325°F oven for 70-75 minutes until a toothpick inserted in the center comes out with a few moist crumbs
Allow cake to cool completely
For the glaze, add butter, milk, and brown sugar to a pan and bring to a boil
Boil for 1-1.5 minutes, then remove from heat
Add 2-2.5 cups powdered sugar and whisk until smooth
Pour glaze over cooled cake and smooth into an even layer
