Heat an electric griddle to 375 degrees.
In a large bowl, whisk together the flour, sugar, baking powder and salt. In a separate bowl whisk together the milk, sour cream, eggs, melted butter and one teaspoon of vanilla.
Pour the egg mixture into the flour mixture and stir together with a spatula until most of the flour is incorporated. Add the sprinkles and mix until batter is free of all flour streaks. Batter will be very thick.
Swirl a bit of butter under each place on griddle where you will be dropping the batter. Drop about 1/4 cup of batter onto hot griddle for each pancake. I used a large cookie scoop for easy release of the batter. Cook until tops are beginning to look dry. You may see a few bubbles, but batter is thick, so you may not. I think these cooked for 6 - 8 minutes on one side before I flipped them. Flip and leave on griddle until cooked through.
To prepare the glaze, put the butter and milk in a glass bowl and microwave until melted. Add the vanilla and pinch of salt and whisk. Add powdered sugar, ¼ cup at a time, whisking after each addition. If glaze still seems too loose, add a little extra powdered sugar.
Serve the pancakes topped with glaze and more sprinkles.