Preheat oven to 400F with rack on lower middle position. Line a 12-cup muffin pan with liners.
In a bowl, whisk together the egg, vanilla, butter, milk, and lemon zest until incorporated. In a separate bowl, whisk together the flour, sugar, baking powder, and salt. Using a rubber spatula, gently fold together the wet and dry ingredients just until combined. A few little streaks of flour is fine. Gently fold in the white chocolate chips and raspberries. If some berries break apart, it is fine.
Divide batter evenly between the lined muffin cups. Sprinkle tops with coarse sugar as desired.
Bake 19-20 minutes or until toothpick comes out mostly clean. A few tender crumbs attached is good.
Let muffins cool completely to room temp.
Melt 1/2 cup white chocolate chips in microwave at 30-second intervals until smooth and creamy. Drizzle over tops of cooled muffins. Muffins will keep 2-3 days at room temp in airtight container.