01 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
02 - In a medium bowl, whisk together the gluten-free rolled oats, flour blend, baking soda, baking powder, ground cinnamon, and fine sea salt until evenly distributed. Set aside.
03 - In a large bowl, beat the softened unsalted butter, coconut sugar, and granulated sugar together using an electric mixer until the mixture becomes light and fluffy, approximately 2 to 3 minutes. Add the egg and pure vanilla extract, beating until fully incorporated.
04 - Gradually add the dry ingredient mixture to the creamed butter mixture, mixing on low speed until just combined. Avoid overmixing to keep the cookies tender.
05 - Scoop approximately 1 tablespoon of dough per cookie onto the prepared baking sheets, spacing each portion about 2 inches apart to allow for spreading.
06 - Bake for 10 to 12 minutes, or until the edges are golden and the centers appear set. Allow the cookies to rest on the baking sheets for 5 minutes before transferring to a wire cooling rack to cool completely.
07 - In a mixing bowl, beat the softened butter with the sifted powdered sugar until light and fluffy. Blend in the heavy cream, pure vanilla extract, and a pinch of fine sea salt until the filling is smooth and creamy.
08 - Once the cookies have cooled completely, spread or pipe a generous layer of vanilla creme filling onto the flat side of one cookie. Place a second cookie flat-side down on top to form a sandwich. Repeat with all remaining cookies and filling.