01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or grease thoroughly with cooking spray.
02 - In a large mixing bowl, whisk together flour, sugar, baking powder, baking soda, and salt until evenly distributed.
03 - In a separate bowl, whisk melted butter, milk, eggs, lemon juice, lemon zest, and vanilla extract until smooth and fully incorporated.
04 - Pour wet ingredients into dry mixture. Gently fold with a spatula until just combined—do not overmix or muffins will become tough.
05 - In a small bowl, beat softened cream cheese with sugar, egg yolk, and lemon zest until smooth and creamy.
06 - Spoon 2 tablespoons batter into each muffin cup. Place 1 heaping teaspoon cream cheese filling in center. Cover with remaining batter, filling cups ¾ full.
07 - Sprinkle coarse sugar evenly over muffin tops for a sweet, crunchy finish.
08 - Bake for 18–22 minutes until golden brown. Test doneness by inserting toothpick into edge (avoid center filling)—it should come out clean.
09 - Let muffins rest in tin for 5 minutes. Transfer to wire rack and cool completely before serving.