Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking pan with baking spray.

In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy, about 3 minutes.

Add the eggs one at a time and mix until fully incorporated.

In another bowl, whisk together the flour, baking powder, baking soda, and salt.

Add the dry ingredients to the butter mixture in three additions, alternating with the sour cream. Begin and end with the dry ingredients. Mix just until combined.

To prepare the streusel, combine the brown sugar, espresso powder, cinnamon, and vanilla extract. Reserve about two-thirds of this mixture for the center layer.

Stir the remaining streusel mixture with the flour and salt. Add the melted butter and mix until crumbly.

Spread half of the Espresso Streusel Coffee Cake batter into the prepared pan.

Sprinkle the reserved espresso sugar mixture evenly over the batter.

Spread the remaining batter over the filling.

Finish with the prepared streusel topping.

Bake for 45–55 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Allow the cake to cool completely before slicing and serving.