Preheat the oven to 350°F (175°C) and line a 12-cup muffin pan with paper liners.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In a separate large bowl, whisk together the melted butter, sugar, eggs, and vanilla extract.
Add the apple cider and sour cream to the wet mixture and whisk until smooth.
Gradually add the dry ingredients to the wet ingredients and stir just until combined.
Divide the batter evenly among the muffin cups, filling each about three-quarters full.
To make the streusel, combine the flour, brown sugar, cinnamon, and salt in a small bowl.
Add the melted butter and mix until the mixture forms coarse, crumbly pieces.
Sprinkle the streusel evenly over each muffin.
Bake for 18–22 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the pan for 5 minutes, then transfer them to a wire rack.
Serve warm or at room temperature.
