01 - Preheat oven to 350°F. Lightly grease a 12-cavity donut pan or line a muffin tin with paper liners.
02 - Whisk together flour, granulated sugar, baking powder, baking soda, and salt in a large mixing bowl until evenly distributed.
03 - In a separate mixing bowl, whisk cooled brewed coffee, whole milk, melted butter, large eggs, and vanilla extract until fully combined.
04 - Pour wet ingredients into the dry mixture and gently stir until just combined. Avoid overmixing to maintain tenderness.
05 - Fold in rainbow sprinkles evenly throughout the batter.
06 - Distribute batter evenly into the prepared donut pan or muffin tin, filling each cavity about three-quarters full.
07 - Bake in preheated oven for 13 to 15 minutes, or until a toothpick inserted into the center emerges clean.
08 - Allow donuts to cool in the pan for 5 minutes, then carefully transfer them to a wire rack to cool completely.
09 - Whisk powdered sugar with 1 to 2 tablespoons of brewed coffee or whole milk until the glaze reaches a smooth, pourable consistency.
10 - Dip the cooled donuts into the glaze and garnish with additional sprinkles as desired.
11 - Let glazed donuts rest for 10 to 15 minutes to allow the glaze to set before serving.