Preheat the oven to 425 degrees F. Place the puff pastry sheet on a nonstick baking sheet. Brush the pastry with the egg wash.

Slice the plums into even slices and place them in a bowl. Sprinkle the sugar over top and stir. Let sit for 5 minutes. Place the plums in clusters of 3 or 4 on the tars – you want to do them in a tic-tac-toe shape on the pastry so it’s easy to cut once baked. Drizzle a bit of the brown butter over top.

Bake for 20 to 25 minutes, until the pastry is puffed and golden. Once finishing, drizzle the remaining brown butter over top and sprinkle the plums with sea salt. Slice into squares and serve immediately.