In a medium bowl, whisk together the gluten-free 1:1 baking flour, almond flour, corn starch, salt, and baking powder.
In a stand mixer fitted with a paddle attachment (or using a hand mixer), beat the butter and almond extract until creamed. Add the powdered sugar and mix until combined.
Scrape down the sides of the bowl, then with the mixer running on low, slowly add the flour mixture. Scrape the bowl down once more and then mix until evenly combined.
Cover the bowl with plastic wrap and refrigerate for 30 minutes.
Preheat to 400 degrees. Line a baking sheet with parchment paper or a silicone baking sheet.
Use a cookie scoop to portion out 2 tablespoon sized dollops. Roll the dough with your hands to create a round ball. Place the dough on the baking sheet then press down slightly and top with 2-3 almond slivers.
Bake for 9-11 minutes, until the cookies just begin to brown around the edges. Let the cookies cool on a baking sheet for 3-5 minutes, then transfer to a wire rack to cool completely. Repeat with the remaining cookie dough.
For the Glaze: In a medium bowl, combine the powdered sugar, water and almond extract. Whisk together and add more water if needed to thin the consistency. Drizzle over the cooled cookies and enjoy!