01 - Preheat oven to 375°F. Grease a 12-cavity donut pan thoroughly with cooking spray or butter.
02 - In a large bowl, whisk together flour, granulated sugar, baking powder, salt, and ground cinnamon until evenly distributed.
03 - In a separate bowl, whisk milk, eggs, melted butter, vanilla extract, and lemon zest until fully combined and smooth.
04 - Pour wet ingredients into dry ingredients. Fold gently until just combined, being careful not to overmix the batter.
05 - In a small bowl, combine melted butter, brown sugar, and cinnamon for the filling, stirring until smooth.
06 - Spoon half of the batter evenly into the prepared donut pan. Create a small ring of cinnamon sugar filling in each cavity, then cover with remaining batter.
07 - Bake for 10-12 minutes until donuts spring back when lightly touched and edges are golden brown.
08 - Let donuts cool in the pan for 5 minutes, then carefully transfer to a wire rack to cool completely.
09 - Whisk powdered sugar, milk, and vanilla extract until smooth and creamy. Adjust consistency with additional milk if needed.
10 - Dip tops of cooled donuts into the glaze. Immediately sprinkle with purple, green, and gold sugars in alternating sections to create traditional King Cake stripes. Allow glaze to set before serving.