01 -
Heat your oven to 325°F and prepare an 8x8 square baking pan by buttering it well or using cooking spray. Line with parchment paper for easy removal later.
02 -
In a large mixing bowl, whisk together ¾ cup of the flour with both sugars, cinnamon, and salt. Pour in the melted butter and gently stir with a fork until it looks mostly combined but still has that perfect crumbly texture. Fold in the remaining ½ cup flour until you have lovely chunky crumbs.
03 -
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt until well combined. Set this mixture aside for now.
04 -
Using a mixer, cream the softened butter and sugar together on medium speed for about 3 minutes until it becomes light and fluffy. Beat in the egg until well incorporated, then scrape down the bowl. Add the sour cream, milk, and vanilla, mixing on medium-low speed until combined - don't worry if it looks a bit curdled at this point!
05 -
With your mixer on low speed, gradually add the flour mixture to the butter mixture, beating just until everything comes together. Don't overmix! Spread this thick batter evenly in your prepared pan, then generously sprinkle all that delicious crumb topping over the surface.
06 -
Bake for 40 minutes, or until a toothpick inserted in the center comes out with just a few moist crumbs clinging to it. If the top starts getting too brown before the time is up, loosely cover with foil. Let the cake cool completely in the pan, then dust with powdered sugar before slicing and serving.