01 -
In a medium bowl, combine 5 tablespoons flour, 4 teaspoons ground cinnamon, and 1 1/2 cups brown sugar. Stir in melted butter until evenly incorporated. Set aside.
02 -
Set oven temperature to 375°F.
03 -
In a large bowl, beat softened butter with 1 1/2 cups white sugar until light and fluffy.
04 -
Add vanilla extract, eggs, whole milk, pumpkin puree, and sourdough discard to the creamed mixture. Blend thoroughly until homogeneous.
05 -
Stir in baking powder and pumpkin pie spice, mixing until combined.
06 -
Gradually add 3 1/2 cups all-purpose flour, one cup at a time, mixing well after each addition until batter is smooth.
07 -
Grease a 9x13 inch pan generously. Spread half of the batter evenly across the pan. Sprinkle half of the cinnamon sugar mixture over the batter. Pour remaining batter on top, then crumble remaining cinnamon sugar over it.
08 -
Bake for 45 to 55 minutes, or until golden brown and a toothpick inserted in the center comes out clean. Allow to cool in pan.
09 -
In a small bowl, blend powdered sugar, 1 teaspoon vanilla extract, and 1 tablespoon milk until smooth. Add up to 1 additional tablespoon milk gradually to achieve desired consistency.
10 -
Drizzle glaze over cooled coffee cake. Slice and serve.