Crust
Put flour, butter and margarine in a food processor. Pulse a few times to start chopping up butter. Then through the feed tube, slowly dribble in (while pulsing) 3-4 tbsp ice water. Keep pulsing until pastry comes together into a shaggy ball – but don’t over-process, you’ll toughen the dough. (Open the lid partway through the water-adding process to feel how your dough is doing, and adjust by adding more or less water.) Remove from processor – don’t knead, just pat together into a ball. Cut dough in half and on a lightly floured board, roll out half the dough to a circle a little larger than your 9" pie plate. Fit the pastry into the pie plate, letting an inch or so of dough hang over. Tuck edges under and press with a fork or flute between your thumb and fingers. Preheat oven to 400ºF. Put pie plate in the freezer to chill for 15 minutes. Then, to blind bake: prick bottom and sides of pastry with a fork and place a generous piece of aluminum foil inside the crust, pressing into the corners and sides. Fill with pastry weights, dry beans or raw rice and bake at 400ºF for 20 minutes. Remove foil, reduce heat to 350ºF and bake an additional 10 minutes, until lightly browned and fairly dry to the touch. Set aside to cool. Reduce oven to 325ºF (to bake meringue later).

Filling
In a medium saucepot, whisk together sugar and cornstarch. Place over med-high heat and whisk in partridgeberry and orange juices, and zest. Continue whisking as the mixture cooks and thickens. Whisk egg yolks in a separate bowl, and while whisking constantly, pour in about a cup of the hot thickened juice mixture, thus tempering the yolks. Scrape the tempered yolks back into the pot and whisk together for a minute. Remove from heat and press though a sieve into the baked, cooled pie shell to strain out any bits of cooked egg and orange zest. Smooth into the shell and set aside.

Meringue
Whip egg whites with cream of tartar and salt until foamy, increase speed to high and slowly pour in sugar. Keep whipping until mixture holds medium peaks. Pour over filling, spreading meringue to edges of crust and pulling up your knife or spatula to make nice swirls and drifts that will brown. Place in 325ºF oven for 15-20 minutes until meringue is browned. Cool to room temperature, then transfer to fridge and chill for 3-4 hours before cutting. Serves 8.