1. Preheat the oven to 350 degrees F. Line an 8 x 8 inch metal baking dish with parchment paper. This makes for easy removal. Set aside.

   You can use a ceramic or glass baking dish, however it will extend the baking time.

Streusel Topping

1. In a small bowl, add the flour, brown sugar, cinnamon and salt. Whisk until combined. Using clean fingers, press the diced cold butter into the flour mixture until the mixture resembles wet sand. Press the crumble topping together to create large crumble pieces. 
   105 grams all-purpose flour, 165 grams brown sugar, 4 grams cinnamon, 1 gram salt, 84 grams unsalted butter, COLD
2. Place the streusel topping in the fridge while you prepare the coffee cake batter.

Sourdough Coffee Cake

1. In a large bowl, add the flour, baking powder, and salt. Whisk until all the ingredients are incorporated. Set aside.
   245 grams all-purpose flour, 6 grams baking powder, 3 grams salt
2. In a bowl of a stand mixer with a paddle attachment, cream together the room temperature butter and sugars on medium speed until light and fluffy, about 2-3 minutes. Beat in the eggs, one at a time, until incorporated. Scrape down the sides when needed. Mix in the sour cream, milk, sourdough discard and vanilla extract on low until smooth. 
   113 grams unsalted butter, room temperature, 100 grams sugar, 55 grams brown sugar, light or dark, 2 large eggs, 8 grams vanilla extract, 160 grams sour cream, room temperature, 120 grams milk, room temperature, 120 grams sourdough discard, room temperature
3. While continuing to mix on low, slowly add in the flour mixture and continue to mix until you see just a few streaks of flour left. Use a rubber spatula to fold in the last bits of flour. Be careful not to over mix the batter, otherwise this will lead to a tough cake. 
4. Scoop half of the batter into the prepared baking dish and spread evenly using an offset spatula. Sprinkle half of the streusel mixture on top for a delicious cinnamon swirl in the center. Then pour the remaining batter on top. I like to use a cookie scoop since the batter is thicker. 

   Note: Be patient while spreading the top layer of batter as it will want to pull up since it is sticking to the streusel. Slowly spread with an offset spatula until evenly spread. 
5. Top the sourdough coffee cake batter with the remaining cinnamon streusel. 
6. Bake the Sourdough Coffee Cake for 50-55 minutes, or until a toothpick comes out with just a few crumbs. 
7. Cool slightly before slicing and serving warm. 

Vanilla Icing

1. In a medium bowl, add the powdered sugar, heavy cream and vanilla extract. Whisk until smooth. Drizzle on top of the Sourdough Coffee Cake and enjoy! 
   130 grams powdered sugar, 90 grams heavy cream, 2 grams vanilla extract