Plums have most definitely arrived at the Greenmarket, and I picked up some Santa Rosas to make these tarts. The tart dough was made with a high ratio of butter and no eggs, which means that its buttery, rich, and quite delicate. You need a spatula to pick up the tarts.
The crumbly topping is the same topping I used to make the blueberry buckle. And it's fairly quick to put together: First, in a medium bowl, mix together all of the dry ingredients: 1 cup all-purpose flour, 1/4 cup demerarra sugar, 1 teaspoon ground cinnamon and 1/4 teaspoon sea salt. Then cube 6 tablespoons cool, unsalted butter and cut the cubes with a pastry blender or fork into the dough (you could also use your fingers). Once the butter is blended into the dry ingredients, use your finger tips to smoosh the mixture together to create large clumps.
The plums were a bit tart and I used a little more sugar than I normally would for the filling and a touch of flour for thickening. I baked them for thirty minutes until the filling was bubbly and the shells were golden.