Preheat oven to 400°F. Line a baking sheet with parchment.

Whisk mascarpone, powdered sugar, and vanilla until smooth.

Toss berries with lemon juice.

Lay one phyllo sheet and brush lightly with butter. Top with another sheet.

Spread a thin line of mascarpone near one edge. Add berries on top.

Roll tightly into a log and place seam-side down.

Brush roll with butter and sprinkle coarse sugar.

Bake 10–12 minutes until golden and crisp. Cool 5 minutes, then slice.