Prepare the crust: Place the butter in a food processor and process a few seconds until creamy. Add the sugar and vanilla and process until the mixture is light and fluffy, about 20 seconds, stopping to scrape the sides of the bowl once or twice.
Combine the four, ground gingersnaps, ginger, and salt in a small bowl and add them to the food processor. Process until the dough comes together around the sides of the bowl, then scrape the sides of the bowl and process for a few extra seconds.
With lightly floured hands, press the dough evenly over the bottom and up the sides of a loose-bottom 9-inch tart pan, pressing particularly around the bottom edge of the pan with your fingers, making sure that the dough is not too thick.
Trim off any excess dough at the top of the tart pan with a knife, then lightly press the dough around the inside of the rim with your thumb so it extends about 1/8 inch above the pan. Prick the dough all over with a fork, then chill the prepared pan, covered with plastic wrap, in the freezer for at least 30 minutes or overnight.
Preheat the oven to 375°F.
Prepare the filling: Place the quartered plums in a bowl with the sugar, ginger, and cinamon. Toss well and set aside.
Bake the chilled or frozen tart shell until golden brown,25 minutes. Cool completely, in the pan, on a wire rack. Reduce the oven temperature to 350°F.
Brush half the jelly all over the inside of the cooled tart shell. Arrange the plums decoratively in the tart shell, skin side up, starting at the outside rim and working toward the center.The plums should overlap slightly. Brush them all over with the remaining jelly.
Place the tart on a baking sheet.Cover the rim of the tart shell with aluminum foil to prevent the crust from overbrowning, then bake the tart until the plums are tender, about 30 minutes. Let cool on a rack to room temperature or until slightly warm, then remove the sides of the pan, place the tart on a serving plate and serve.