01 -
Pulse cold butter and shortening into the flour, sugar, and salt using a food processor until reduced to pea-sized pieces. Transfer to a large bowl. Sprinkle the water and vinegar mixture over the surface and toss with a fork until just incorporated. Form into 2 balls, wrap in plastic, and chill in the fridge.
02 -
Roll out one dough ball into a 12-inch round and place into a 9- or 10-inch deep pie plate. Tuck excess pastry under edges and flute edges with fingers or a fork. Wrap foil around the crust edge and blind bake with weights for 15 minutes at 375°F. Remove weights and parchment paper.
03 -
Add the mixed fruit and berries with the sugar to a medium saucepan. Simmer for 10-15 minutes, stirring gently. Add dissolved corn starch, stirring until thickened. Adjust corn starch as needed based on the juice content. Set aside to cool slightly.
04 -
Rub flour, brown sugar, cold butter, baking powder, cinnamon, and oats together with hands until fully combined.
05 -
Add the cooled fruit filling to the blind-baked crust. Sprinkle crumble topping evenly over the filling. Bake at 350°F for 1 hour or until the filling is bubbly. Cover crust edges with foil if browning too quickly.
06 -
Allow the pie to cool for at least 1 hour before slicing and serving. Optionally, serve with vanilla ice cream.