Preheat your oven to 350 degrees, then prepare the filling and crumb topping separately in their own small bowls by simply mixing their ingredients. Set aside. 

For the cake, fully mix the butter and sugar together in a large mixing bowl. Crack the eggs in and beat well. Then add the vanilla, sour cream and baking powder and soda. Mix until all ingredients are fully incorporated.

Add the flour and mix until just combined – be careful not to over mix.

Generously butter a baking dish and pour in half of the cake batter, then spread it out evenly on the bottom of the baking dish.

Sprinkle the filling evenly over this bottom layer of cake batter.

Carefully pour in the remaining batter over the filling. Try to cover as much of the filling as possible as you’re pouring the last of the batter, but don’t worry if you don’t cover everything perfectly – we’ll spread it evenly in this next step!

I happened to have a miniature spatula (which I use to scrape up the last bit of product in bottles), but if you don’t have a mini spatula on-hand, use your smallest spatula or the back of a small spoon to spread the top layer of cake batter over the filling, smoothing over imperfections and ensuring the batter now fully covers the filling.

Then sprinkle the crumb topping evenly as the last layer of this beautiful coffee cake.

Pop this into your preheated oven and bake for 50-55 minutes. Once you poke a toothpick into the coffee cake and it comes out clean, you’ll know this beauty is done baking.

Allow the coffee cake to cool for 15 minutes, then cut into about 15 portions and serve.