Preheat a griddle or cast-iron skillet over low heat.
In a medium bowl or large liquid measuring cup, beat the egg with a fork until frothy, about 30-60 seconds. If making a vegan version, skip this step.
Add the milk, oil or melted butter, vinegar, and vanilla and mix with the fork until combined.
Add the buckwheat flour, salt, baking soda, and baking powder and mix them in with the fork until just combined, about 1 minute. Do not over-mix the batter or the pancakes won't rise as much.
Once the skillet is preheated melt 1 tablespoon of butter to coat the bottom of the pan. Add more butter as needed if using a larger griddle.
Using an ice-cream scoop or a serving spoon, drop 1 scoop of batter into the pan at a time. A 12-inch cast iron skillet will fit 3 pancakes at a time. The batter should sizzle as it hits the pan.
Sprinkle a heaping tablespoon of blueberries over the top of each pancake then add a tiny bit more of the batter to cover the berries so they don't scorch when the pancakes are flipped over.
Cook the pancakes until bubbles start to form, about 2 minutes, then flip them over with a spatula. Adjust the heat as needed throughout the process.
Cook them for another 1-2 minutes then transfer them to a platter that has been warmed under hot water or in a warm oven to keep them warm while the rest of the batches are cooked.
Repeat the process until all of the buckwheat pancake batter is used up. Serve them hot with butter, warmed maple syrup, and fresh fruit if desired.