1-Brown the butter: Melt 1 cup (227g) unsalted butter in a skillet over medium heat, stirring frequently until golden brown and fragrant (about 7-10 minutes). Immediately pour into a heat-safe bowl, discard the dark solids, then add the remaining 2 tablespoons (28g) unsalted butter. Let cool.

2-Prep the oven and pan: Preheat oven to 350°F (175°C). Grease an 8-inch square pan and line with parchment paper, leaving an overhang for easy removal.

3-Make the crumb topping: Whisk together flour, brown sugar, granulated sugar, cinnamon, and salt. Stir in half the browned butter until the mixture clumps without flour streaks. Set aside.

4-Mix dry ingredients for cake: In a large bowl, mix the flour, cinnamon, baking powder, baking soda, and salt.

5-Prepare wet ingredients: In another bowl, whisk together remaining browned butter, brown sugar, egg, maple syrup, sour cream, and vanilla extract if used.

6-Combine batter: Add dry mixture to wet ingredients and fold gently just until blended to keep the cake light.

7-Assemble and bake: Pour batter into prepared pan and sprinkle crumb topping evenly over the top. Bake 40-50 minutes or until a toothpick inserted comes out with moist crumbs.

8-Cool the cake: Allow cake to cool completely in pan on a wire rack.

9-Prepare maple icing: Whisk powdered sugar with maple syrup until smooth. Thin with water or milk as needed for drizzle consistency. Drizzle over cooled cake before slicing.