Preheat oven to 350 degrees. Position oven rack in middle of oven. Set aside an ungreased 15x10x1-inch jelly roll pan.
Place the cake mix, softened butter, and cream cheese in a large bowl. Blend for 2 minutes with an electric mixer set on low speed until blended and a crumbly dough forms. Gather dough together and press into jelly roll pan. Bake crust for 10 minutes.
Meanwhile, place the brown sugar, buttermilk, eggs, ½ cup melted butter, flour, and vanilla extract in a large bowl and mix with an electric mixer set on low speed until well blended. Stir in almonds. Pour mixture over partially baked crust.
Bake for 25-28 minutes or until golden brown and firm to the touch. Transfer to wire rack and cool completely before cutting into squares. Sprinkle cooled squares with powdered sugar.