Prepare the Baking Sheet: Line a baking sheet with parchment paper and preheat the oven to 400°F (200°C).

Mix Dry Ingredients: Sift together gluten-free flour, baking powder, poppyseeds (if using), and kosher salt.

Create Lemon-Sugar Mixture: Combine granulated sugar with fresh lemon zest and rub the zest into the sugar until fragrant.

Combine Ingredients: Fold the dry ingredients into the lemon-sugar mixture.

Cut in the Butter: Add cold, cubed butter and work it into the mixture until it resembles coarse crumbs.

Incorporate Wet Ingredients: Whisk together kefir (or buttermilk), egg, and fresh lemon juice, then stir into the dry mixture until just combined.

Shape the Dough: Transfer dough onto a floured surface, pat into a rectangular shape, and fold in thirds like a letter, repeating twice.

Chill the Dough: Shape dough into a 6-inch round disk, wrap in plastic wrap, and refrigerate for at least 10 minutes.

Prepare for Baking: Cut chilled dough into eight wedges and place on the prepared baking sheet.

Brush and Sprinkle: Brush tops with kefir and sprinkle generously with raw sugar.

Bake the Scones: Bake for 22-26 minutes or until golden brown.

Cool and Glaze: Let cool on a wire rack and drizzle with a glaze made of powdered sugar and lemon juice.