In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, and salt until well mixed.

In a separate bowl, blend the buttermilk, Greek yogurt (or sour cream), melted butter, and vanilla extract. Stir until smooth and creamy.

Gently fold the wet ingredients into the dry ones, mixing just until combined.

Carefully add the blueberries to the batter, folding them in with a spatula.

In a deep frying pan, heat avocado oil over medium heat until it reaches approximately 350°F.

Drop spoonfuls of the batter into the hot oil, frying them until golden brown for about 3-4 minutes per side.

Once golden, remove the donut holes and let them drain on paper towels.

In a separate bowl, whisk together the melted butter, lemon juice, granulated sugar, lemon zest, powdered sugar, cultured buttermilk, and vanilla extract until smooth.

Dip each warm donut hole into the lemon glaze, allowing the excess to drip off. Set aside on a wire rack to let the glaze set for a few minutes.