In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In a separate medium bowl, whisk together the buttermilk, milk, egg, melted butter, and vanilla extract until well combined.
Pour the wet ingredients into the dry ingredients and gently stir until just combined. Do not overmix; the batter should be slightly lumpy.
Carefully fold in the fresh blueberries, distributing them evenly throughout the batter.
Heat a large non-stick skillet or griddle over medium heat and add 1 tablespoon of butter. Allow it to melt and coat the surface.
Pour 1/4 cup of batter onto the skillet for each pancake. Cook until bubbles form on the surface and the edges look set, about 2-3 minutes.
Flip the pancakes and cook for another 2-3 minutes, until golden brown and cooked through.
Transfer cooked pancakes to a warm plate and repeat the process with remaining batter, adding more butter to the skillet as needed.
Serve warm with maple syrup or your favorite pancake toppings.