Melt 5 tablespoons of butter in the microwave. Set aside to cool to room temperature. Make sure the milk and egg are also at room temperature so the butter does not clump.
Pour the vinegar into a liquid measuring cup. Add milk until it reaches the 1-1/4 cup line. Stir and let sit for 5 minutes so it slightly curdles. Add the egg and vanilla and whisk until smooth.
In a large bowl, whisk together the flour, sugar, salt, baking powder, baking soda, and cornstarch.
Pour the milk mixture and melted butter over the dry ingredients. Use a spatula to scrape in every bit. Whisk gently for no longer than 30 seconds. Some lumps are fine. Let the batter rest for 10 mins.
Heat a nonstick skillet over medium heat or preheat an electric griddle to 300°F. Once hot, rub the remaining 3 tablespoons butter across the pan using tongs or a paper towel.
Use a 1/4-cup measuring cup to scoop batter onto the griddle. The batter should spread into about a 4-inch circle. If needed, gently spread it with a spoon. Immediately press blueberries into the batter (as few or as many as you'd like!). Cook until bubbles form across the surface. Use a thin spatula to flip and cook the other side until golden brown. If the butter or pancakes begin browning too quickly, reduce the heat.
Wipe the pan with a paper towel, add more butter, and continue cooking until all the batter is used. To keep pancakes warm while cooking, see note 3.
Serve pancakes immediately with syrup and toppings of choice.
Notes
Note 1: This recipe calls for 8 tablespoons of butter. 5 tablespoons are melted for the batter. The remaining 3 tablespoons can be used to grease the pan for cooking the pancakes.Note 2: To make my favorite syrup, combine 1/2 cup unsalted butter, 1 cup light brown sugar, 1/2 cup heavy cream, and a pinch of salt in a medium pot. Cook over medium heat, stirring occasionally, until butter melts and syrup slightly thickens, about 5–8 mins. Remove from heat; stir in 1 tablespoon vanilla extract.Note 3: Place a cooling rack on a large sheet pan. As soon as pancakes come off the skillet, place them in a single layer on the rack. Keep the pan in a 200°F oven while cooking the remaining pancakes.Storage: Let pancakes cool, then stack with wax paper between each. Store in an airtight container in the fridge for up to 3 days or freeze for up to 2 months. Reheat in the microwave or toaster.