Preheat the oven to 350ºF (180ºC). Line the bottom of an 8-inch square cake pan with parchment paper. Grease and flour the insides.

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

In a large bowl, beat the butter, brown sugar and granulated sugar together, with an electric mixer on medium speed, until pale and fluffy. Beat in the eggs and maple extract in three additions, making sure each one is incorporated before adding the next.

In a small bowl, whisk together the milk and sour cream until well blended. Stir the flour mixture into the batter by hand, in two additions, followed by half of the milk mixture after each addition. Mix just until combined. Do not over mix. Gently stir in the blueberries.

Transfer the batter to the prepared cake pan. Smooth the top with a spatula. Bake until a toothpick inserted into the center comes out clean, about 25-30 minutes. Do not over bake. Let the cake cool in the pan for 10 minutes, then remove the cake from the pan and transfer it to a cooling rack. Serve warm or at room temperature.

In a small saucepan over medium heat, cook the blueberries, maple syrup, salt and 1/3 cup (78ml) of water until the blueberries are softened, about 3-4 minutes. In a small bowl, create a slurry by whisking together the cornstarch with the remaining 1 tablespoon (15ml) of water. Stir the slurry into the blueberry mixture. Continue cooking and stirring until thickened, about 1-2 more minutes. Remove from heat and set aside to cool.

In a large bowl, whip the heavy whipping cream, with an electric mixer at medium speed, until frothy. Add the powdered sugar and vanilla. Continue whipping, at medium-high speed, until medium peaks form. Do not over whip. Cover and refrigerate until ready to use.