01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the gluten-free oats, flour blend, baking soda, baking powder, cinnamon, and sea salt. Set aside.
03 - In a large bowl, beat the softened butter with coconut sugar and granulated sugar using an electric mixer until light and fluffy, approximately 2 to 3 minutes. Add the egg and 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 dough in roughly 1-tablespoon portions onto the prepared baking sheets, spacing each mound 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 cookies to rest on the baking sheets for 5 minutes, then transfer to a wire 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 sea salt until the filling is smooth and creamy.
08 - Once the cookies have cooled completely, spread or pipe a generous layer of 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 the remaining cookies and filling.