Mix flour, sugar, baking powder and salt in a bowl. Stir in the room-warm butter and work into a dough. Press out the dough into a spring shape with removable edges, about 24 cm in diameter.
Bake pie shell for 10 minutes so it gets some color.
Mix sugar and pectin. Divide strawberries and rhubarb into suitable pieces and mix with the sugar and pectin mixture.
Divide the berries in the pie shell and bake for 15 minutes.