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. Set aside.
03 - In a large bowl, beat the softened butter, coconut sugar, and granulated sugar with an electric mixer until light and fluffy, about 2 minutes. Add the egg and vanilla extract, beating until fully incorporated.
04 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
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 brown and the centers appear set. Allow cookies to rest on the baking sheets for 5 minutes, then transfer 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, vanilla extract, and a pinch of 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. Press a second cookie flat-side down onto the filling to form a sandwich. Repeat with all remaining cookies and filling.