Step 1: Reduce the Apple Cider – Pour the apple cider into a small saucepan over medium-high heat. Simmer the cider until it has reduced to exactly 1/2 cup. This should take about 10 to 12 minutes. Set it aside to cool slightly before using it in the batter.
Step 2: Preheat and Prepare – Preheat your oven to 350°F (175°C). Grease a standard 12-cup muffin tin with non-stick spray or line it with paper liners. If using liners, a light spray inside the liners can help the muffins release more easily.
Step 3: Mix the Dry Ingredients – In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, ground cinnamon, salt, and nutmeg. Ensure there are no large clumps of flour or spices for a consistent texture.
Step 4: Combine the Wet Ingredients – In a separate medium bowl, whisk together the egg, granulated sugar, and brown sugar until smooth. Stir in the milk, the cooled reduced apple cider, the 1/4 cup of melted butter, and the vanilla extract until well combined.
Step 5: Create the Batter – Gently pour the wet ingredients into the dry ingredients. Using a spatula, fold the mixture together until just combined. Be careful not to overmix, as this can lead to tough muffins; a few small lumps are perfectly fine.
Step 6: Bake the Muffins – Divide the batter evenly among the 12 muffin cups, filling each about three-quarters full. Bake for 15 to 18 minutes, or until a toothpick inserted into the center comes out clean. Let the muffins cool in the pan for about 5 minutes.
Step 7: Apply the Topping – While the muffins are cooling, mix the 1/2 cup of sugar and 1 tablespoon of cinnamon in a small bowl. Melt the remaining 1/4 cup of butter in another bowl. Remove a warm muffin from the tin, brush the top with melted butter, and then roll it in the cinnamon sugar mixture until well coated. Repeat for all muffins.