Combine 1/3 cup sugar, flour, and ground flax seeds in a food processor; pulse until blended. Add butter and egg yolk; pulse until mixture is crumbly and starts to hold together. Add Sherry or water, pulsing until dough forms a ball. Press into a disk in between two pieces of wax paper. Chill 30 to 60 minutes.
Preheat oven to 400°. Line bottom (not sides) of a 9-inch metal tart pan (or glass or ceramic baking dish) with parchment paper. Roll dough between wax paper until it is slightly large than tart pan. Peel off one side of wax paper. Flip dough into pan, peeling off second piece of paper. Press into tart pan, patching any holes. Trim edge. Dock pastry with a fork. Bake 10 minutes until just barely golden (do not over bake). Cool.
For the filling, combine 1/2 cup sugar, egg, vanilla, and cream cheese in a food processor. Process until smooth and well blended. Pour into baked crust. Reduce heat to 325° and bake 20 to 25 minutes or until filling has puffed up slightly and lightly browned. Remove from oven; cool completely.
Brush top of pie with a thin layer of jam. If the strawberries are large (California-size, cut in half sideways and place them on the tart, following the outline of the crust). If the strawberries are smaller, you can remove the top and place the berries on the tart “tip-up” if you like. Brush lightly with the remaining jam and serve.