For the jam: Set a sieve over a medium bowl. Trim the ends from the oranges, then cut away the peel and pith. Working over the bowl to catch the juice, cut along the membrane on both sides of each orange segment with a paring knife and let the segments drop into the sieve. Squeeze the juice from the leftover membranes into the bowl. Remove the segments from the grapefruits in the same manner, and squeeze the juices from the leftover membranes into the bowl. Remove the segments from 1 lemon and squeeze the juice from the leftover membranes into the bowl. Squeeze the juice from the remaining lemon into the bowl.

Place the citrus segments, juices, sugar and arrowroot in a medium saucepan. Bring the mixture to a boil over medium-high heat, then reduce the heat and simmer until thick, 1 to 1 1/2 hours. Let cool at room temperature for 30 minutes, then refrigerate for 30 minutes.

For the crust: In the bowl of a food processor, combine the flour, sugar, salt and lemon zest. Pulse until blended. Add the butter and pulse until the mixture resembles a coarse meal. Combine the ice water and almond extract. With the machine running, gradually add the water mixture and process until moist clumps form. Turn the dough out onto a work surface and form into a ball. Flatten the dough into a disk and wrap in plastic wrap. Chill for 30 minutes.

Position a rack in the center of the oven and preheat the oven to 375 degrees F.

On a large sheet of parchment paper, roll out the dough into a 10-inch round. Slide the dough and parchment onto a large, heavy baking sheet. Fold in the edge of the dough to make a border, forming an 8 to 9-inch round. Pleat the edge loosely and pinch to seal any cracks in the dough. Prick the bottom of the crust with a fork.

Bake until the crust is golden, about 40 minutes. Let cool on a wire rack for 10 minutes, then slide a metal spatula under the crust and remove the parchment. Let cool completely.

For the topping: In a small bowl, mix together the mascarpone cheese, sugar, vanilla and the orange and lemon zests until smooth.

Spread the mascarpone topping over the cooled crust, then spoon the citrus jam on top. Cut into wedges and serve.