1. Make the Crust Dough:

• Put the flour in a large bowl.
• Gradually work in the shortening with a pastry cutter or two knives until the mixture resembles coarse meal.
• Beat the egg with a fork in a small bowl.
• Pour the egg into the flour mixture.
• Add the cold water, vinegar, and salt.
• Stir until all the ingredients are combined.

2. Chill the Dough:

• Divide the dough in half.
• Form into two balls.
• Place each ball in a large resealable plastic bag.
• Using a rolling pin, slightly flatten each ball of dough.
• Seal the bags and place them in the freezer for 15 to 20 minutes to chill.

3. Prepare the Filling:

• Meanwhile, in a large bowl, toss the sliced rhubarb with the apricot jam, vanilla extract, and salt.
• Whisk the sugar and cornstarch together in a small bowl.
• Add the sugar mixture to the rhubarb and mix well. Set aside.

4. Preheat and Prepare the Bottom Crust:

• Position a rack in the lower third of the oven and preheat to 425°F (220°C).
• Roll out one piece of dough into a 12-inch round on a lightly floured surface.
• Place the dough in a 9-inch pie plate. Do not trim the excess dough yet.

5. Add the Filling:

• Pour the rhubarb mixture into the pie plate and spread it evenly.

6. Prepare the Lattice Top:

• Roll out the second piece of dough into a 12-inch round.
• Cut the dough into 12 even strips.
• Lay 6 strips across the top of the pie, evenly spaced.
• Gently fold back every other strip halfway.
• Lay another strip of dough on the pie over the unfolded ones, perpendicular to them.
• Unfold the strips so they lie over the perpendicular one.
• Fold back the strips that haven’t been folded yet and add another perpendicular strip.
• Unfold the strips over it.
• Repeat the folding and unfolding process until you have a lattice. If the dough strips tear, gently press them back together.   

7. Trim and Crimp the Edges:

• Trim the ends of the lattice strips.
• Fold the overhanging bottom crust up and over the lattice strips.
• Trim any uneven areas.
• Crimp the edges decoratively.

8. Brush and Bake:

• Brush the lattice with the heavy cream.
• Sprinkle with sugar.
• Place the pie on a foil-lined baking sheet (to catch any drips).
• Bake on the lower oven rack for 15 minutes.
• Reduce the oven temperature to 375°F (190°C) and continue baking until bubbly and golden brown, about 45 minutes more.
• Tent the pie with foil if it starts getting too brown.

9. Cool Completely:

• Let the pie cool completely on a wire rack before slicing and serving. This allows the filling to set properly.