- 1 sheet frozen puff pastry, thawed
- Granulated sugar, for sprinkling
- 1/2 cup brown sugar
- 1/4 cup orange juice
- 1 teaspoon vanilla extract
- 1/2 teaspoon fennel seeds, lightly crushed
- 3/4 pound rhubarb stalks, diagonally sliced 1/8-inch-thick
- 1/2 cup mascarpone, at room temperature
Preheat oven to 400° F. Line a baking sheet with parchment paper.
Gently roll out pastry on a lightly sugared surface. With a sharp knife, score a 1/4-inch border around the whole sheet (do not cut through pastry). Put pastry on the prepared baking sheet and refrigerate while preparing filling.
Mix together brown sugar, juice, vanilla and fennel in a bowl. Add rhubarb and stir to coat. Let stand for 20 minutes, stirring occasionally. Strain rhubarb mixture, reserving 2 tablespoons liquid.
Spread mascarpone in a thin layer over puff pastry (within border). Top mascarpone with rhubarb slices, overlapping slices slightly. Drizzle with 2 tablespoons reserved liquid.
Bake until pastry is puffed and rhubarb is tender, about 30 minutes. Let cool slightly and cut into squares; serve warm.