In a bowl, add the milk and vinegar. Let it sit for about 5 minutes. Set aside.
In a mixing bowl, add in the flour and salt. Stir until combined.
Cut in the shortening until it's cut into small pea size pieces. You can use two forks to cut it in or a pastry cutter.
Add in the milk and vinegar mixture into the flour and stir until combined.
Flour a clean surface. Dump the pie crust onto the floured surface and roll it out. It can tear super easy. Use a spatula to release the crust from the surface. Pick it up and place it in an 8 inch pie pan. Cut off any excess crust.
Poke several holes in the bottom of your crust using a fork.
Place in the oven and bake for 12 - 15 minutes until golden brown.
Remove from the oven and let cool completely.
In a large pan, add in the sugar and cornstarch. Whisk to combine.
Add in the rhubarb and 3 cups of blueberries. Place over medium heat and let cook. Using a spatula or potato masher, mash down the blueberries. This will help release the juices and help the process.
Let the blueberries cook, stirring occasionally for about 20 minutes until the blueberries become a thick sauce. Run a spoon along the bottom of the pan. If you can get it across the bottom of a large saucepan before it starts filling back in, the filling is ready. Remove from the heat and let cool completely. You can place it in the fridge to hurry the process.
Stir in the extra 1 and 1/2 cups of blueberries into the cooled filling.
Pour the filling into the cooled crust.
Place about 2 inches of water in a saucepan. Let it simmer and place a heat proof mixing bowl on top of the saucepan. Make sure the water isn't touching the bottom of the bowl.
Place the eggs whites and sugars into the mixing bowl. Whisk the whites and sugar until combined and foamy. Once the egg whites reach 140 °F, remove from the heat
Beat the egg whites until they form soft peaks. Add in the cream of tartar and pinch of salt.
Continue to beat the egg whites until they become glossy and forms stiff peaks.
Spread the meringue on top of the cooled pie. Make sure the meringue touches all sides of the crust. Form any designs in the meringue. I ran a knife in swirls on my meringue. You can also place the knife on the meringue and pull up and give the pie spikes.
Using a torch or the oven boiler, brown the top of the meringue. Watch it like a hawk, because it can burn very quickly.
Place in the fridge to chill for 4-5 hours to overnight. Cut and serve.
Blueberry Rhubarb Meringue Pie https://www.cookiedoughandovenmitt.com/blueberry-rhubarb-meringue-pie-3/