Directions

Make the biscuit dough

In a large bowl, combine the sweet rice, almond, oat and tapioca flours with the ¼ cup sugar, baking powder and salt. Whisk to combine.
Add the butter slices and lemon zest. Blend with a pastry cutter or your fingertips until the butter is broken down into the size of small peas.
Whisk together the 6 tablespoons milk and egg in a measuring glass.
Gradually add the milk mixture to the flour mixture, working with a flexible silicone spatula until the dough holds together when you give it a squeeze. If the dough is too dry, add a few more drops of milk directly to the floury bits. Knead the dough a few times in the bowl to bring it together into a ball. 
Gently but firmly press the dough together with your hands and shape it into a rough ball. Place on a piece of beeswax wrap or plastic wrap and press it into a disk that measures about 6 inches across. Don't worry about overworking the dough since there isn't any gluten to toughen here!
Wrap and chill the dough disk until firm, at least 30 minutes and up to overnight.
While the dough chills, rinse and dry the berries, cutting them in half if they’re very large.

Shape & Bake

When ready to bake, position a rack in the upper third of the oven and preheat to 350ºF. Butter the bottom and sides of an 8-inch (20-cm) round or square cake pan with softened butter and line the bottom with a round of parchment paper cut to fit.
Remove the dough from the refrigerator and place on a large piece of parchment paper dusted lightly with oat flour. Use your hands and a rolling pin to pat and roll the dough out into a 14x10" (25x350cm) rectangle, dusting the dough as needed to prevent sticking. If the dough cracks or breaks at any point, don’t worry, just pinch and squish it back together. 
When the dough begins to stick to the parchment, top with a second sheet of parchment and, grasping both pieces of parchment and the dough, bravely flip the whole thing over. Gently peel away the top piece of parchment and continue rolling out the dough. 
Sprinkle the blueberries evenly over the dough; use your palms to press them gently into the dough and sprinkle with 1-2 teaspoons of sugar. 
Starting with a long end, use the parchment to help roll the dough into a log, rolling it as tightly as possible and ending with the seam side down. 
Use a sharp chef’s knife to cut the log into 8 equal pieces (if using a round pan) or 9 pieces (if using a square pan), cutting straight down in an assertive manner. Place each round with a cut side up in the prepared pan, using a thin spatula to help transfer the biscuits if needed. Gently press the tops of the biscuits to flatten them slightly. At this point, you can cover and chill the biscuits up to overnight.
Brush the tops of the biscuits with a little milk or cream and sprinkle with a bit more sugar to encourage browning. 
Bake the biscuits until golden and cooked through, 40–55 minutes. Remove from the oven and let cool to warm, 20-30 minutes.

Finish & Serve

Invert a large plate over the pan, turn the pan over to release the biscuits, and remove the parchment round. Invert another plate on top of the biscuits and turn them right side up. 
Make the icing by whisking together the powdered sugar, mascarpone and enough lemon juice to make a drizzle-able glaze.
Spoon the glaze over the warm buns and sprinkle with crumbled freeze-dried berries and bee pollen, if using. Serve warm or at room temperature.
The biscuits are best within a few hours of baking, but extras will keep, airtight at room temperature, for an additional day, or refrigerated for up to 3 days. Re-warm before serving.