Preheat oven to 425ºF. Put a glass mixing bowl in the freezer.
Line a baking sheet with parchment paper. Add the puff pastry, and use a table knife to draw a small border line (~½" wide) on the outside of the pastry. Take care to not cut all the way through the dough!Note: This recipe was written for refrigerated puff pastry. If using frozen puff pastry, thaw before using, rolled out to ¼" thickness, and work on a floured surface instead of parchment paper.
Add quince, orange or lemon juice, and half the sugar to a bowl and toss. Drain off the juice.
Arrange the quince in a single layer on the puff pastry, leaving the border empty. (Some overlapping fruit is okay.)
Brush the beaten egg along the border and any other exposed pastry. Tip: Make sure to avoid getting egg on the sides of the pastry, because it will keep the puff from rising.
Bake about 15 minutes, or until the puff is golden.
While the puff bakes, take the mixing bowl out of the freezer. Add the orange or lemon zest, mascarpone, cream cheese, and remaining sugar to the bowl. Use an electric hand mixer set to high, and beat the mixture until it forms stiff peaks.
Cool the tart for about 5 minutes, sprinkle the tart with almonds, and serve with a dollop of mascarpone whip.
Leftovers:This tart is best right after baking, but leftovers can be stored in the fridge 1-2 days. Eat leftovers cool, or bake for 3-5 minutes to warm it up.