Whisk together the starches and flours to make the gluten-free flour blend. If using a stand mixer, mix all the ingredients with the paddle attachment for 3 minutes.

Stir together the oat milk (300 g) and psyllium, then let it hydrate for 2-3 minutes.

Stir the instant yeast into the oat milk (80 g) with 1/4 of the sugar until dissolved.

In a large mixing bowl, combine the gluten-free flour blend, baking powder, sugar, and salt. Mix well.

Combine the liquids (oat milk, beaten eggs, olive oil, and dissolved yeast). Mix them into the dry ingredients until a rough dough forms, then add the orange zest and apple cider vinegar.

Mix the dough by hand until smooth, uniform, and shaped into a ball. Alternatively, knead it for 4-5 minutes in a stand mixer fitted with the dough hook. Scrape down the sides and bottom of the bowl from time to time with a rubber spatula to make sure no flour remains unincorporated.

Cover the dough with a damp kitchen towel or plastic wrap, then let it rise in the refrigerator for 45-60 minutes.

Gently deflate the chilled dough and transfer it to a floured work surface. Knead lightly for 2-3 minutes, until smooth, adding a little more flour if the dough is still sticky.

Divide the dough into 15 equal pieces, about 70 g each, or into 10 larger buns, about 110 g each.

Shape the dough by cupping your hand into a "claw" and moving it in a circular motion against the work surface. Pull the edges of the dough inward toward the center to shape each piece into a ball. That circular motion against the surface will help create a smooth, round shape.

Place the shaped dough balls on a baking sheet lined with parchment paper. Cover with a damp kitchen towel or plastic wrap. Let rise in a warm place for 60-90 minutes, or until doubled in size.

Preheat the oven to 180°C. In a small bowl, beat 1 egg with a spoonful of oat milk, then brush the buns with the egg wash. This will help them develop a golden crust.

Bake the buns for 20-22 minutes, or until golden brown.

Let the buns cool slightly before serving. Serve warm with your favorite spreads or fillings.