This is a stunningly beautiful dessert: Paper-thin slices of plums or pluots rest atop a layer of almond paste, which is nestled in a puff pastry case - sure to please almond lovers! Elegant and unusual, this dessert will wow your guests, even though it's so easy to make. Serve with whipped cream or Crème Anglaise for a memorable summer dessert.
Line a baking sheet with a piece of parchment paper. Roll out the puff pastry on the parchment paper into a roughly 9 x 8-inch rectangle. With the tip of a knife, lightly draw a line around all four sides of the pastry about 1/2 inch from the outer edges of the dough. Don't cut through the pastry. With a fork, pierce the inside area of the pastry.
On another piece of parchment paper, roll out the almond paste to form a rectangle that will fit within the scored area of the puff pastry, roughly 8x7 inches in size. Carefully transfer the almond paste to the puff pastry.
Position a rack in the middle of the oven and preheat to 400 degrees F.
Set the pluots, stem side up, on a cutting board. Cut the pluots vertically (parallel to the cleft in the fruit) into very thin rounds (1/8 inch), starting on one side of the fruit and working toward the middle. When you reach the pit, begin slicing on the other side to create pretty rounds. Discard the pits and the small bit of fruit that clings to them. Discard (or eat) the first rounds if they’re small.
Arrange the pluot slices in neat rows atop the almond paste, overlapping the rounds slightly and covering all of the almond paste. Don’t let the fruit extend onto the marked edges of the puff pastry.
In a small saucepan, bring the plum jam and 1 tablespoon of water to a simmer over low heat, stirring until the jam is melted. Cook until the mixture forms a syrup, 3 to 5 minutes. Lightly brush the pluots with the jam syrup. Brush the unadorned edges of the pastry with the egg wash.
Transfer the galette to the oven and bake until the pastry is puffed and golden, 20 to 30 minutes. Cool before slicing.