Preheat oven to 350 degrees F. Line an 8×8 baking pan with parchment paper and spray with nonstick baking spray that contains flour.
In a medium size bowl whisk together the flour, baking powder, baking soda, and kosher salt.
1 1/2 cups All-purpose flour, 1/4 tsp Baking powder, 1/4 tsp Baking soda, 1/2 tsp Kosher salt
In a large bowl combine the sugar and lemon zest. Using your fingers, rub the zest into the sugar until combined. Add the butter and cream together for 3-4 minutes using an electric mixer until it is light and fluffy.
1 cup Granulated sugar, 3 tbsp Lemon zest, 1/2 cup Unsalted butter
Add the eggs and lemon juice and beat until well combined. Add the sour cream and hand stir until incorporated.
3 large Eggs, 2 tbsp Fresh lemon juice, 1/3 cup Sour cream
Add the dry ingredients, half at a time, and stir by hand until just incorporated. Pour the batter into the prepared pan and spread out evenly. Remove the crumb topping from the freezer, break it up with a fork or spoon, and sprinkle it evenly over the top of the cake batter.
Bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely and dust it with powdered sugar for a prettier appearance if desired.