01 - Preheat oven to 350°F. Grease and line an 8-inch square baking pan.
02 - Whisk together flour, baking powder, baking soda, and salt for the cake layer.
03 - Beat softened butter and granulated sugar until light and fluffy.
04 - Add eggs one at a time, then mix in vanilla extract.
05 - Alternately add dry ingredients and milk to the butter mixture. Stir until just combined.
06 - Pour batter into prepared pan, smooth surface, and bake for 25-28 minutes until a toothpick comes out clean. Allow to cool completely in the pan.
07 - Whip heavy cream with powdered sugar and vanilla until stiff peaks form.
08 - Spread whipped cream evenly over cooled cake layer.
09 - Combine flour, brown sugar, and cold cubed butter. Rub together until coarse crumbs form. Stir in chopped nuts if desired.
10 - Sprinkle topping evenly over cream layer and bake an additional 7-10 minutes until golden brown.
11 - Cool at least 15 minutes before slicing and serving.