Preheat your oven to 350°F (175°C). Line your baking sheets with parchment paper for easy cleanup and to prevent the cookies from sticking.
In a medium bowl, whisk together the gluten free flour, cornstarch, baking powder, salt, and baking soda. Set this mixture aside.
In a large mixing bowl, beat the softened unsalted butter and granulated sugar together using an electric mixer on medium speed until light and fluffy, about 2-3 minutes.
Add the large egg, vanilla extract, and almond extract (if using) to the butter mixture. Beat until well combined.
Add the sour cream to the wet mixture and mix until smooth.
Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Avoid overmixing.
Using a cookie scoop or tablespoon, drop heaping spoonfuls of dough onto the prepared baking sheets, leaving space between each cookie.
Bake for 10-12 minutes or until edges are lightly golden. Centers may look slightly underbaked. Cool on baking sheets for a few minutes before transferring to a cooling rack to cool completely.