• Lightly grease and flour a  9x13 inch pan. Preheat the oven to 350F degrees. 

Make the Filling and Streusel

• In a medium bowl stir together the flour, brown sugar & cinnamon.
• Stir in the melted butter until the mixture resembles wet sand.

Make the Cake Batter

• In a medium bowl whisk together the flour, baking powder, baking soda & salt. 
• In a large bowl using an electric mixer beat the butter and sugar until fluffy. (about 2 minutes).
• Mix in the eggs 1 at a time, then mix in the vanilla extract.
• In a liquid measuring cup whisk together the sour cream and milk.
• With the electric mixer on low speed beat about 1/3 of the flour mixture into the butter mixture, alternating with about 1/3 of the sour cream and milk. 
• Repeat the process until combined, turning off the mixer and scraping down the sides of the bowl as necessary.

Assemble & Bake

• Spoon about 1/2 of the cake batter into the bottom of the prepared pan. Smooth the top.
• Sprinkle about 1 cup of streusel mixture on top of the cake batter.
• Spoon the remaining cake batter over top of the struesel, then gently spread it over top.
• Crumble the remaining streusel over top of the cake batter. 
• Bake in the preheated oven for 30-35 minutes or until an inserted toothpick comes out clean and the cake doesn't wobble if you give the pan a gentle nudge.
• Allow the cake to cool for at least 30 minutes before cutting into it.

Glaze

• In a small bowl whisk together 1 cup powdered sugar with 3 tablespoons of cream.
• If it seems to thin, add a little more powdered sugar. If it's too thick, add in a little more cream about 1 teaspoon at a time.
• Drizzle over top.