In a small saucepan over medium heat, combine 2 tablespoons of water, 1 cup of blueberries, and ½ cup of granulated sugar. Stir until combined and let it cook until the blueberries start to burst and release their juices, creating a sauce.
In a separate small bowl, mix ⅓ cup of water with 1 tablespoon of cornstarch to make a slurry. Once the blueberry compote is hot, slowly add the slurry while stirring continuously. The mixture will turn a light purple at first—keep cooking until it darkens and thickens. This helps cook out the raw cornstarch flavor.
Remove from heat and let the compote cool to room temperature. Place plastic wrap directly on top to prevent a skin from forming. As it cools, it will thicken more. If you want to speed up the process, pop it in the fridge.
For the cookies:
Preheat the oven to 375°F (190°C) and line two baking sheets with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment (or a large bowl with a hand mixer), cream the slightly chilled butter, granulated sugar, and light brown sugar on medium speed until light and fluffy, about 2-3 minutes. This step helps the cookies hold their shape.
Scrape down the sides of the bowl, then add the whole egg and mix for 30 seconds. Scrape down the bowl again, add the egg yolk, and mix for another 30 seconds.
Add the maple syrup, vanilla extract, and butter extract, mixing on low speed until combined. Scrape down the sides of the bowl as needed.
Add the all-purpose flour, salt, cornstarch, baking soda, baking powder, and cornmeal to the bowl. Mix on low speed until just combined, being careful not to overmix.
Using a 4-tablespoon cookie scoop, portion out the dough and place it on the prepared baking sheets, spacing them about 2 inches apart. Gently press each dough ball down slightly to flatten, aiming for about a 3-inch diameter with a flat top.
Bake for 8-10 minutes, or until the edges are lightly golden and the centers are set. The cookies will continue to firm up as they cool. Let them rest on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.
For the maple buttercream:
In a medium bowl, beat the softened butter with an electric mixer on medium speed until smooth and creamy. Add the powdered sugar and mix on low speed until fully incorporated. Pour in the maple syrup and a pinch of salt, then mix on medium speed until the buttercream is light and fluffy.
To assemble:
Once the cookies are completely cool, use a 1-tablespoon scoop to place a dollop of maple butter in the center of each cookie. Lightly press down the top of the dollop with the back of a spoon. Spoon a bit of the blueberry compote over the maple butter. If you’re feeling extra, drizzle a little maple syrup on top for the perfect finishing touch!