In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until evenly combined with no lumps.
In a separate bowl, whisk the eggs, buttermilk, melted butter, and vanilla extract until smooth and well blended.
Pour the wet ingredients into the dry ingredients and stir gently with a spatula just until combined. The batter should be slightly lumpy — do not overmix. Let the batter rest for 5 minutes.
Gently fold the blueberries and diced strawberries into the batter, being careful not to crush the berries or overmix.
Heat a large griddle or non-stick skillet over medium heat and lightly grease with butter or oil. Test the heat by sprinkling a few drops of water — they should sizzle gently.
Pour 1/4 cup of batter per pancake onto the hot griddle, spacing them 2 inches apart. Cook until bubbles form across the surface and the edges look set, about 2-3 minutes.
Flip the pancakes carefully and cook until the second side is golden brown and the center is cooked through, another 1-2 minutes.
Transfer cooked pancakes to a plate and keep warm in a 200°F oven while you finish the remaining batter. Serve immediately with your favorite toppings.
