Stir the flour and salt together. Cut in the lard with a pastry blender or 2 knives until the shortening is in pea size pieces.
In a liquid measuring cup, combine the egg and vinegar. Add enough cold water to make one cup.
Stir the liquid ¼ cup of the liquid into the flour mixture, adding just enough to make the dough cling together. You might not use all of the water.
Mix with a wooden spoon until mixed thoroughly, then gather the dough into a ball. Cover and refrigerate for one hour, you can chill overnight, covered, providing you leave it at room temp for 15 mins before rolling.
On a lightly floured surface, roll into a circle and place in a 9-inch pie plate. Crimp edges and chill until ready to fill.
Toss the rhubarb & strawberry filling together. Fill the chilled pie shell with the rhubarb & strawberry filling. Place your pie crust on top, either a whole piece or lattice. Make sure there are pie vents cut into the top if you use the whole piece. Crimp the edges together. Preheat the oven to 400 °F.
Bake the pie on a tray at 400°F for 20 minutes, then reduce heat to 350°F and bake for about 40 minutes more until the filling is bubbling.
If the crust edge is browning too quickly, cover edges with a thin strip of tin foil. Brush the top of the pie crust with a beaten egg yolk 10 minutes before you are ready to remove it from the oven.
Allow the pie to cool for 10-15 minutes.
Serve with vanilla ice cream. Makes 8-10 servings.