Small Italian prune plums work best for this recipe and are in season, so they should be easy to find at the market.
11/2 cups flour
1/3 cup icing sugar
1/2 tsp salt
1/2 tsp cinnamon (optional)
3/4 cup cold unsalted butter, cubed
500 g (1 lb) prune plums, about 12
1/4 cup brown sugar
1 tsp grated lime zest
1/4 cup chopped pistachios (optional)
Preheat oven to 350 F.
Line an 8-inch square cake pan with parchment paper, leaving an overhang.
Mix together flour, icing sugar, salt, cinnamon and butter in a food processor or by hand until well blended. The mixture will look like fine breadcrumbs. Place 2 cups in a bowl and gently combine. Gently pat into an 8 x 8 greased pan. Prick with a fork. Bake for 20 minutes or until the pastry is a creamy gold.
Slice the plums into quarters lengthwise. Remove pits and stems. Toss gently with brown sugar and lime zest. Arrange plums on the crust skin-side up. Squeeze them in to fit. Add chopped pistachios to remaining crumbly dough (if desired), and sprinkle on top of fruit.
Bake for 30 to 40 minutes or until top is golden, mixture is bubbling and fruit is tender. Remove from oven and cool in pan on a wire rack until room temperature. Lift from pan and cut into squares.