Preheat the oven to 400F.
In a large bowl, stir together the flour, sugar, baking powder and salt. In a smaller bowl or measuring cup, stir together the melted butter or oil, eggs, milk and orange zest. Add to the dry ingredients and stir until almost combined; add the cranberries and stir just until blended.
Fill paper-lined muffin cups and bake for 20-25 minutes, or until golden and springy to the touch. Makes about 1 dozen muffins.