01 - Preheat oven to 350°F. Grease a standard 12-well donut pan with cooking spray or butter.
02 - In a large mixing bowl, whisk together flour, granulated sugar, baking powder, ground cinnamon, salt, and lemon zest until well blended.
03 - In a separate bowl, whisk eggs, whole milk, melted butter, and vanilla extract until smooth and fully incorporated.
04 - Pour wet ingredients into dry ingredients. Stir gently with a spatula until just combined—batter will remain slightly thick. Avoid overmixing to prevent tough donuts.
05 - In a small bowl, stir together melted butter, brown sugar, and ground cinnamon until sugar is dissolved and mixture forms a paste.
06 - Spoon half the batter into prepared donut wells, filling each about one-third full. Create a small well in center of each, add a swirl of cinnamon sugar filling, then cover with remaining batter.
07 - Bake for 10–12 minutes until tops spring back lightly when touched and edges are golden brown. Cool in pan for 5 minutes before transferring to wire rack.
08 - Whisk powdered sugar, milk, and vanilla extract in a small bowl until completely smooth. Adjust consistency with additional milk if needed.
09 - Dip tops of cooled donuts into glaze, allowing excess to drip off. Immediately sprinkle with purple, green, and gold sprinkles while glaze is wet.
10 - Let glaze set for at least 10 minutes at room temperature before serving. Donuts are best enjoyed the same day but can be stored in an airtight container for up to 2 days.