Preheat the oven to 350°F. Coat a standard 12-cup metal muffin tin generously with vegetable oil spray, then dust each cup lightly with flour to ensure a flawless release.

In a medium bowl, sift together the all-purpose flour, baking powder, kosher salt, ground nutmeg, and baking soda to aerate the dry ingredients and ensure even distribution.

In a separate small bowl, whisk the whole milk and buttermilk together until unified.

In the bowl of an electric stand mixer, vigorously cream the softened butter and granulated sugar together on medium-high speed until the mixture is highly aerated, pale, and fluffy. Add the eggs one at a time, followed by the vanilla extract, mixing thoroughly.

Remove the bowl from the mixer. Using a heavy wooden spoon, gently stir one-quarter of the dry flour mixture into the butter emulsion. Follow immediately with one-third of the milk mixture.

Continue this alternating sequence, folding strictly until the ingredients are just combined. Do not overwork the batter, or the gluten will overdevelop and destroy the tender, doughnut-like crumb. The resulting dough will be exceptionally thick and sticky.

Use a heavy-duty ice cream scoop to portion the batter evenly into the prepared muffin cups, filling them nearly to the top to encourage a high dome.

Bake in the preheated 350°F oven until the tops are golden brown and firm to the touch, about 30 to 35 minutes.

Remove the muffin tin from the oven and allow the muffins to cool for 5 minutes before carefully transferring them to a wire rack.

In a small, shallow bowl, whisk together the ¾ cup of granulated sugar and the ground cinnamon.

While the muffins are still warm, use a pastry brush to coat the entire exterior (top, sides, and bottom) of each muffin heavily with the melted butter.

Immediately roll the buttered muffins in the cinnamon-sugar mixture until a thick, shattered, crystallized crust forms. Serve warm.