In a large mixing bowl, combine sweet rice flour, blanched almond flour, gluten-free oat flour, tapioca flour, sugar, baking powder, and fine sea salt. Whisk to ensure all dry ingredients are evenly mixed and free of lumps.

In a separate bowl, whisk together the lemon zest, whole milk, and egg until thoroughly combined. Gradually pour the wet mixture into the dry ingredients, stirring gently until just combined.

Carefully add the fresh blueberries to the dough, folding them in gently to prevent bursting. Ensure they are evenly dispersed throughout the dough.

On a lightly floured surface, shape the dough into a rectangle about 1-inch thick. Use a knife or biscuit cutter to cut out biscuits.

If you prefer to bake later, cover the baking sheet with plastic wrap and refrigerate the dough overnight.

Preheat your oven to 400°F (200°C). Once heated, bake the biscuits for 20-25 minutes, or until golden brown.

While the biscuits are baking, whisk together powdered sugar and fresh lemon juice in a small bowl until smooth.

Once the biscuits have cooled slightly, drizzle the prepared icing over the top and garnish with optional toppings.