In a large bowl whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a medium bowl wish together the sugar, eggs, zest, juice, and milk. Whisk in the butter.
Gently fold the wet ingredients into the dry ingredients until just combined.
Fill each muffin cup with two tablespoons of muffin batter. Then add two teaspoons of Grapefruit Spread and top with another tablespoon of batter. Evenly distribute any left over batter amongst the muffin cups.
Bake for 20 minutes or until the edges appear golden brown.
Allow to cool and top with powdered sugar. Store in an airtight container for up to a week.