The plums or plumcots in this tart are layered atop a no-bake honey ginger mascarpone cheesecake filling, nestled in a browned butter crust. The browned butter crust is adapted from America's Test Kitchen.
Place rack in center of the oven and preheat oven to 350 degrees Fahrenheit.
Whisk flour, sugar, and salt together in a bowl.
Melt the butter in a small stainless steel saucepan over medium-high heat, swirling occasionally, until the foam eases up. When the butter solids begin to turn golden and the butter has a nutty, toasted aroma, remove the pan from the heat and add the water. The mixture will bubble up. When the bubbling eases up, add the browned butter to the flour mixture and stir to create a dough.
Transfer the dough to a 9-inch square or 10-inch round fluted tart pan with removable bottom. Set aside for 10 minutes, until the dough is just warm.
Press the dough evenly across the bottom and up the sides of the tart pan. You will use about 2/3 of the dough for the bottom and 1/3 for the sides.
Place the pan on a wire rack set on a baking sheet, and bake until the crust is golden brown, about 25 to 30 minutes, rotating the pan halfway through.
Allow the baked crust to cool for at least an hour.
Using a microplane grater, grate the ginger into a fine-mesh strainer set over a small bowl. Press the grated ginger to extract the ginger juice. Discard the solids. Set the ginger juice aside.
Using an electric mixer, whip the mascarpone and heavy whipping cream together until stiff peaks form. Transfer this mixture to another bowl and set aside.
Again using the electric mixer (no need to clean the bowl or beaters), blend the cream cheese with the ginger juice and honey. Then fold in the reserved mascarpone mixture. (Taste the mixture--if you would like it to be sweeter, fold in a bit more honey or a few teaspoons of sugar.)
Spread the filling in the cooled tart crust, and place in the refrigerator to chill for at least three hours.
Slice the plums, plumcots, or pluots as desired, and layer the slices atop the chilled mascarpone filling. Store in the refrigerator until ready to serve. (It will be best served the same day.)