In a large bowl, whisk together the flour, granulated sugar, baking powder, and salt. In another bowl, whisk together the buttermilk, melted butter, vanilla, and eggs. Add the wet ingredients to the flour mixture, then whisk to combine. Cover and refrigerate overnight.
The next day, thin the batter with the milk (use less milk if you want thicker, denser pancakes). Lightly spray the inside of your pancake mold with nonstick cooking spray, then coat a griddle or nonstick pan with a little softened butter. Place the mold onto the griddle, and heat over medium-high heat.
Ladle 1/3 cup of batter into each mold. You may need to hold the mold in place until the batter begins to cook. Once bubbles begin to form on top of the batter (about two minutes), remove the molds and use a spatula to flip the pancakes to the other side. Transfer pancakes to plate and repeat with the rest of the batter.
Tip: you can keep the pancakes warm by covering with a clean kitchen towel, or by heating your oven to 200°F and placing the pancakes on a baking sheet.
Serve with warm maple syrup, a dusting of powdered sugar, and fresh strawberries or other berries.