Preheat the oven to 425°F. Grease or line two standard muffin pans with paper liners.
In a large mixing bowl, whisk together 3 cups of all-purpose flour, 1 ½ tablespoons baking powder, 2 teaspoons cinnamon, ¼ teaspoon nutmeg, and 1 teaspoon kosher salt until evenly combined.
In a separate large bowl, whisk together 1 cup melted butter, ¾ cup granulated sugar, and ½ cup brown sugar. Add 3 eggs and whisk until combined. Add 1 cup sour cream and 1 teaspoon vanilla extract, whisking until smooth.
Add half of the dry ingredient mixture to the wet ingredients, alternating with ½ cup of apple cider. Gently fold together until just combined. Add the remaining dry ingredients and remaining ½ cup apple cider, folding gently until incorporated. Do not overmix! A few small lumps or flour streaks are okay.
Let the batter rest for 10–15 minutes to allow the flour to absorb the moisture.
Divide the batter evenly between two parchment lined 9x5-inch loaf pans, spreading it into an even layer. Bake at 350°F for 40–50 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
While the loaves bake, combine ¾ cup granulated sugar and 2 teaspoons cinnamon in a shallow bowl. Mix until evenly combined.
Pour the cinnamon sugar mixture onto a jelly roll pan or large rimmed baking sheet, spreading it into a generous, even layer. Brush the cooled loaf all over with melted butter, then carefully roll it through the cinnamon sugar, turning as needed to coat all sides. Sprinkle additional cinnamon sugar over any bare spots until the loaf is evenly coated.
Serve warm, slice and enjoy!