Gather the ingredients.
To make the doughnuts, preheat oven to 375 F. Grease and lightly flour a large doughnut pan or 2 small doughnut pans for a total of 12 doughnuts.
In a large mixing bowl, sift together the cake flour, sugar, baking powder, nutmeg, and salt.
In a separate bowl whisk together the buttermilk, eggs, melted butter, and vanilla until well combined.
Add the wet ingredients to the dry and stir until just combined.
Fill a piping bag with the batter and pipe the batter into the doughnut pan. Bake until golden brown and fragrant, about 12 minutes.
Remove from the oven. Cool doughnuts in the pan for five minutes then invert onto a cooling rack. Cool fully before glazing and decorating.
To make the glaze combine the powdered sugar, milk, and vanilla in a mixing bowl and whisk until smooth.
Divide the glaze into multiple bowls. Add different food coloring to each bowl and mix well. Dip the top half of each doughnut in the icing, allow the excess to drip off, then return to the rack, icing side up. Top with sprinkles.
Melt the white chocolate wafers according to the instructions on the bag. Using a fork or chopstick, drizzle or flick the melted chocolate across the doughnuts. Serve immediately.