1 (14 to 16 ounce) package prepared pie crusts, thawed if frozen- or make your own.

1 large egg 

1 teaspoon water

3/4 pounds chopped rhubarb (about 3 cups / 3 stalks), 

3 cups Sliced Strawberries

3/4 cup caster sugar

1/2 teaspoon ground cinnamon

1/4 cup potato starch plus 1/8 c

3 or 4 large fresh mint leaves

1/4 teaspoon sea salt

Chilled butter cubed to top the pie filling

2 tablespoons demerara sugar

Tips:

You can use fresh or frozen rhubarb for this recipe. 

Just be sure to thaw the frozen rhubarb first. About an hour at room temperature does the trick.

Protect the pie crust with an egg wash, both inside and out. 

Sprinkle the sugar mixture described below and then put in refrigerator while you are making the filling and rolling out the top crust.  Use the remaining egg wash as a sealer for the top crust.

Venting is key for a perfect rhubarb filling. Rhubarb has a surprising amount of moisture, and the sugar draws it out. 

Make sure you’ve got plenty of vent holes — either make them with a circle cutter, or top the pie with a lattice. Venting allows moisture to leave the pie as steam, and prevents sogginess. 

Use potato starch instead of flour or tapioca or any other thickener. I do 1:1 as out lined in any fruit recipes, plus an extra hand full.  

Depending on the size of the leaves, roll up 3 or 4 large leaves of mint, chiffonade the leaves, very, very small.  It virtually melts in the pie.

Finally, include dabs of butter on top of the filling.

Finish the pie before baking with course sugar, demerara.

Place a baking sheet in the oven as the oven preheats. 

When you add the pie to the oven, set the pie on the preheated baking sheet.
This initial blast of heat will help crisp the bottom crust.
The baking sheet will catch any bubbling filling that leaks out.