In a medium-size bowl, mix the flour, brown sugar, cinnamon and salt. Work in the butter with your fingertips until the mixture looks sandy with no large pieces of butter remaining. Press the mixture together to make chunks. Set aside in the refrigerator until ready to use.

Preheat the oven to 350ºF (180ºC). Line a 9-inch square cake pan* with parchment paper, leaving a couple of inches of overhang.

In a medium-size bowl, whisk together the flour, baking powder, salt, cinnamon and nutmeg until well blended.

In a large bowl, cream the butter, brown sugar and granulated sugar, with an electric mixer on medium speed, until light and fluffy. Beat the eggs into the butter mixture in two separate additions, making sure each one is incorporated before adding the next. Beat in the extracts until combined.

In a small bowl, whisk the milk and sour cream together. On low speed, beat the flour mixture into the batter in three additions, alternating with the milk mixture. Mix just until combined.

Transfer the batter to the prepared pan. Smooth the top with a spatula. Set aside 1/4 cup (38g) of blueberries. Top the cake batter evenly with the remaining blueberries, then the topping mixture. Top with the reserved blueberries. Bake until a toothpick inserted into the center of the cake comes out clean, about 25-30 minutes. Do not over bake. Cool the cake in the pan. Remove the cake from pan and transfer it to a serving platter.**

In a small bowl, whisk together the powdered sugar, maple syrup, butter, maple extract, salt and 1 tablespoon (15 ml) of milk until well combined. Add additional milk as needed to reach the desired consistency. Whisk until smooth. Drizzle the icing over the cooled cake.