Adapted from My Recipes
Grease and flour a 9x13 inch pan.
Cream the butter until creamy.
Add the sugar to the butter and mix well.
Add eggs and beat well.
Sift flour, baking powder, baking soda and salt.
Add the flour mixture to the butter/sugar mixture, alternating with buttermilk. Begin and end with flour.
Stir in vanilla extract.
Pour the batter into the prepared pan.
Cover the pan tightly with saran wrap and chill for 8 hours or up to 24.
Preheat the oven to 350 degrees and bring the cake up to room temperature for 30 minutes.
Sprinkle the batter with the streusel mixture.
Bake 30-35 minutes or until a tooth pick comes out clean.
Combine powdered sugar, vanilla and milk in a bowl and stir until smooth.
Drizzle the glaze over the top of the cake.