Cinnamon Crumb Mixture

• 2/3 cup brown sugar
• 3/4 cup flour
• 2 1/2 tsp ground cinnamon
• 6 Tbsp unsalted butter, cold and cubed

Cake

• 1 1/3 cups flour
• 1 tsp baking powder
• 1/4 tsp baking soda
• 1/4 tsp salt
• 1/2 cup unsalted butter, room temperature
• 3/4 cup sugar
• 2 eggs
• 2 tsp vanilla extract
• 1/2 cup sour cream
• 2 Tbsp milk

Vanilla Icing (Optional)

• 1 cup icing sugar
• 1/2 tsp vanilla extract
• 2 Tbsp whipping cream or milk

1. Preheat oven to 350°F (177°C). Grease an 8-inch square pan
2. Combine the brown sugar, flour, and cinnamon together in a medium bowl. Cut in the chilled butter until the mixture is in pea-sized crumbs. Refrigerate until step 5.
3. Whisk the flour, baking powder, baking soda, and salt together in a large bowl. Set aside.
4. In another large bowl, beat the butter and sugar together on high speed until smooth and creamy, about 2 minutes. Add the eggs and vanilla, and beat on medium-high speed until combined. Beat to combine. Mixture will be lumpy.
5. Add the flour mixture to the wet ingredients, and beat on low speed until just combined. Beat in the milk.
6. Spread half of the batter into the prepared pan. Sprinkle half of the crumb mixture evenly on top. Spread the remaining batter on top. Sprinkle the remaining crumb mixture evenly on top.
7. Bake for 32–38 minutes or until the cake is baked through. Set the pan on a wire rack to cool.
8. Whisk all of the icing ingredients together. Drizzle over warm cake.
9. Serve!
10. Cover leftovers tightly and store at room temperature for up to 3 days, or in the refrigerator for up 1 week.