On a lightly floured piece of parchment paper, roll out pie crust disk into an oval about 15 by 6-inches and just under 1/4-inch thick. Use a paring knife or pastry cutter to trim any rough edges. Move parchment sheet and crust to a baking sheet. Dock crust with a fork to prevent it from puffing up too much in the oven. Brush the surface of the crust from edge to edge with egg wash.
Bake the dough until it is deep golden brown, 25 to 30 minutes. Check on the crust halfway though baking and if any bubbles have appeared, use a spatula to press them flat. Cool the crust completely on the pan.
While crust cools, combine mascarpone and 2 tablespoons of the sugar. Hull strawberries and slice into 1/4-inch slices.
Move cooled pie crust to a serving platter or board and spread mascarpone over the top in an even layer, dot with jam, then arrange sliced strawberries in a single, slightly overlapping layer in a decorative pattern. Sprinkle tart with the remaining tablespoon of sugar (omit this final sprinkling if your strawberries are particularly sweet), slice, and serve immediately.