Preheat oven to 425° F (218° C). Line 2 half sheet rimmed baking trays with parchment or silicone baking mats.

In a medium bowl, whisk mascarpone cheese, egg, lemon zest, and vanilla bean paste until smooth and creamy.

Unroll puff pastry on a silicone rolling mat or lightly floured countertop. With a sharp chef’s knife, trim to 10 x 10 inches square.

Slice pastry corner-to-corner, forming 4 triangles. Repeat with the second sheet of pastry for 8 triangles total.

Arrange on prepared trays.

Spoon mascarpone filling in the middle of each triangle. Spread with a small stepped palette knife or the back of a spoon, allowing 1 1/2-inch border around the edge.

Arrange peach slices on top of the mascarpone.

With a pastry brush, lightly brush the pastry border with beaten egg, then fold the edges inward. Brush the folded edge with more of the beaten egg.

With kitchen shears, trim away any long pieces of pastry.

Bake in preheated oven for 25-30 minutes, rotating trays halfway through. Continue baking until pastry turns flaky and golden brown, with cheese and peach juice bubbling around the edges.

Cool on trays. Before serving, drizzle with honey. Sprinkle with thyme leaves and dust with confectioner’s sugar. Serve warm or at room temperature.

Wrap leftover peach pastries in foil. Store in the refrigerator for up to 2 days.