Make-ahead Coffee Cake Mix

Make-ahead Coffee Cake Mix (makes enough for two 9 inch cakes)
from Ellen's kitchen, thanks to Cook's Country

Ingredients:

• Streusel:
• 1/3 cup packed (2 1/3 oz) brown sugar
• 1/3 cup (2 1/3 oz) granulated sugar
• 1/3 cup (1 2.3 oz) all purpose flour
• 4 tbs unsalted butter, cut into 1/2 inch pieces and chilled
• 1 tbs ground cinnamon
• 1 cup walnuts, pecans, or almonds, chopped
• Cake:
• 3 cups (15 oz) all purpose flour
• 1 cup packed (7 oz) brown sugar
• 1 cup (7 oz) granulated sugar
• 1/2 cup (2 1/2 oz) buttermilk powder
• 2 tsp baking powder
• 1/2 tsp baking soda
• 1 tsp ground cinnamon
• 1/4 tsp salt
• 12 tbs unsalted butter, cut into 1/2 inch pieces and chilled
• Wet ingredients (for one 9 inch round cake)
• 3/4 cup warm milk
• 2 large eggs
• For the Streusel:
• Using fingers, combine brown sugar, granulated sugar, flour, butter, and cinnamon in bowl until mixture resembles coarse meal.  Stir in nuts.  Freeze in zip lock bag for up to two months.
• For the Cake:
• Process flour, brown sugar, sugar, granulated sugar, buttermilk powder,  baking powder, baking soda, cinnamon, and salt in food processor until combined, about 30 seconds.  Add butter and pulse until mixture is uniform and resembles wet sand, about 15 pulses.  Freeze in zip lock bag for up to 2 months.  
• To make one 9 inch round:
• Adjust oven rack to middle position and heat oven to 325 degrees.  Grease 9 inch round cake pan, line bottom with parchment paper, grease parchment paper, and flour pan.  Using stand mixer fitted with paddle, beat 3 3/4 cups prepared cake mix, warm milk (about 110 degrees),  and eggs on low speed until combined, about 1 minutes.  Increase speed to medium high and beat until mixture is completely smooth, about 3 minutes.  Scrape batter into prepared pan, top with 1 1/3 cups streusel, and bake until toothpick inserted in center comes out clean, 40-45 minutes, rotating pan halfway through baking.  Cool cake in pan on wire rack for 15 minutes.  Invert cake onto large plate (cake will be streusel side down).  Remove pan, place wire rack on top of cake, reinvert cake, streusel side up.  Cool for 30 minutes and serve.
• Apple Spice Coffee Cake:
• Add 1/2 tsp each ground ginger and cardamom to dry cake mix and substitute warm apple cider for milk.
• Blueberry Lemon Coffee Cake:
• Fold 1 cup blueberries and 1 tsp grated lemon zest into batter before scraping into pan and topping with streusel.
• Chocolate Chip Coffee Cake:
• Stir 1 cup chocolate chips into batter before scraping into pan and topping with streusel.
•