Preheat your oven to 350°F (175°C).
Grease your muffin tin with a little butter or line it with muffin liners.
In a large mixing bowl, whisk together the all-purpose flour, sugar, baking powder, and salt.
In another bowl, combine melted butter, sour cream, egg, orange juice, and orange zest. Mix until smooth.
Pour wet ingredients into dry ingredients. Gently fold until just combined.
Spoon the batter into the muffin tin, filling each cup about two-thirds full.
Bake for 18-20 minutes, or until a toothpick comes out clean.
Let muffins cool in the tin for 5 minutes, then transfer to a cooling rack.
Whisk together powdered sugar, orange juice, and additional zest for the glaze. Drizzle over cooled muffins.
