Preheat the oven to 400°F and line a 12-cup standard muffin pan with paper liners or spray with gluten-free nonstick cooking spray.
Add the sugar and lemon zest to a large bowl. Rub the zest into the sugar to release the natural oils.
Whisk in the flour, xanthan gum, baking powder, baking soda, and salt to the sugar/zest, then set aside.
In a medium bowl, whisk together the ricotta, egg, milk, oil, lemon extract, and lemon juice.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Evenly divide the batter between the 12 muffin cups. Bake for 14-16 minutes. Let cool in the pan for 5 minutes before transferring the muffins to a wire rack to finish cooling.
To make the glaze, whisk together the powdered sugar, lemon zest, and lemon juice. Drizzle over the cooled muffins.