Preheat oven to 375 degrees F (190 degrees C).

Place a foil-lined sheet pan on a lower oven rack.

Wash and stem the Concord grapes.

Squeeze the pulp out of the skins into a saucepan, saving the skins in a bowl.

Cook the pulp in a saucepan over medium-low heat, stirring frequently, until the seeds are beginning to come out.

Strain the pulp into the skins, using a spoon to rub the pulp off the seeds.

Add sugar, flour and lemon juice to the grape skins and pulp mixture.

Fit pastry into a 9-inch pie pan.

Pour filling into crust.

Use remaining pastry to make a lattice top.

Bake in the preheated oven on the sheet pan for about 50 minutes, or until the crust is golden brown and filling is bubbly.

Let cool before serving.