Step 1

Stir the flour, salt, and sugar together in a large bowl. Add the butter pieces and coat with the flour mixture using a bench scraper or spatula.

Step 2

With a pastry blender, cut the butter into the flour mixture, working quickly until mostly pea-size pieces of butter remain (a few larger pieces are okay).

Step 3

Combine the water, cider vinegar, and ice in a large measuring cup or small bowl. Sprinkle 2 tablespoons of the ice water mixture over the flour mixture, and mix and cut it in with a bench scraper or spatula until it is fully incorporated.

Step 4

Add more of the ice water mixture, 1 to 2 tablespoons at a time, using the bench scraper or your hands (or both) to mix until the dough comes together in a ball, with some dry bits remaining.

Step 5

Squeeze and pinch with your fingertips to bring all the dough together, sprinkling dry bits with more small drops of the ice water mixture, if necessary, to combine.

Step 6

Divide the dough into halves, shape the dough into flat discs, wrap in plastic, and refrigerate for at least 1 hour, preferably overnight, to give the crust time to mellow

Step 7

After 1 hour, take one of the dough discs out of the fridge. Leave to soften for 5-10 minutes so that you don’t crack the dough and roll it out on a floured work surface (keep the other one in the refrigerator). Turn the dough about a quarter turn after every few rolls until you have a circle 30 cm (12 inches) in diameter. Carefully place the dough into a 22cm (9 inches) diameter pie dish and place back into the fridge.

Step 8

Remove the second dough from the drive and roll out as described previously into a circle roughly 12-inches in diameter. This time placed the dough on a tray and refrigerate. This will be the lid for our pie.

Step 9

Place the rhubarb, strawberries, and lemon zest into a bowl. Combine the sugar and salt in a separate bowl and stir into the fruit. Set the filling aside and let macerate for 30 minutes.

Step 10

Drain the juice from the filling and stir in the cornstarch. Set aside

Step 11

Spoon the filling into the crust.

Step 12

Cover the filling with the 30 cm (12-inch) diameter pie dough circle. Press the top and bottom pie dough overhang together, then using a pair of kitchen shears, trim the edges of both pie crusts until they overhang the edge of the pie plate by 1.5 cm (1/2 an inch) all the way around.

Step 13

Fold overhang under itself to form a thick rim; Tuck top edge under bottom edge and crimp: with thumb and index finger of one hand, gently press dough against knuckle of other hand; continue around the pie.

Step 14

Cut five vents in the top crust for steam. Refrigerate pie for at least 30 minutes to set the crimp.

Step 15

Preheat the oven to 220°C (428F).

Step 16

Prepare the egg wash by mixing the egg, salt and milk and brush top crust with egg wash and bake the pie on the bottom shelf of the oven for 20 minutes.

Step 17

Reduce the temperature to 190°C (374F) and bake for at least a further 1h05 or until you can see the thickened juices bubbling out of the vents. I cooked mine for another 10 minutes for a deeper golden color on the top of the pie, but this will depend on your oven. Stay close to your oven during baking. If the top starts to get too dark, tent it (cover with foil) to avoid overbaking.