01 - Preheat oven to 375°F. Generously grease a 12-cavity donut pan with cooking spray or butter.
02 - In a large mixing bowl, whisk together flour, granulated sugar, baking powder, salt, and ground cinnamon until well combined.
03 - In a separate bowl, whisk whole milk, eggs, melted butter, vanilla extract, and lemon zest until fully incorporated.
04 - Pour wet mixture into dry ingredients. Stir gently with a spatula until just combined—batter should remain slightly thick. Avoid overmixing to prevent tough donuts.
05 - In a small bowl, stir together melted butter, brown sugar, and cinnamon until smooth and uniform.
06 - Spoon half the batter evenly into donut cavities. Create a small ring of cinnamon filling in each cavity, then cover with remaining batter.
07 - Bake for 10-12 minutes until donuts spring back when touched and edges turn golden brown.
08 - Let rest in pan for 5 minutes, then carefully transfer to wire rack to cool completely before glazing.
09 - Whisk powdered sugar, 2 tablespoons milk, and vanilla until smooth. Add remaining milk if needed to achieve pouring consistency.
10 - Dip cooled donut tops into glaze, allowing excess to drip off. Immediately sprinkle purple, green, and gold sugars in alternating sections. Let glaze set for 15 minutes before serving.