Make the compote: Simmer berries (with 1/2 cup berry juices) and other compote ingredients (start with smallest amount of sugar), except cornstarch and water, over medium-high heat, until berries burst and it looks saucy – about 10 minutes. Taste for sweetness and add more sugar if necessary. Dissolve cornstarch into water to make a slurry. Stir into bubbling compote and allow to thicken (couple of minutes) until glossy and the consistency of (lumpy) gravy. If too thin, mix up a little more cornstarch slurry. If too thick, add a little reserved blueberry juice or water. Transfer to a bowl and chill.

Make the crust: Place flour, cornmeal, sugar and zest in food processor; pulse to blend (if you don’t have a blender, use a pastry blender or two forks for these pastry steps). Add butter and pulse until butter is the size of large peas. Then, while continuing to pulse, drizzle in lemon juice and then start drizzling in ice water. Stop every so often to check the dough – pinch a bit between your fingers to see if it holds together; if not, drizzle-pulse in a little more water. You want it to just hold together but not be wet. Remove from food processor and roll into a log (don’t knead). Cut into 8 equal portions. Flatten each piece of crostata dough into a 1/2" thick disc, wrap with plastic wrap and chill a half hour to let gluten in the dough relax.

Preheat the oven to 375°F. Roll out each disc of dough to a circle about 1/4" thick and 6" around. Don’t stress if they aren’t perfectly round. Transfer them to a parchment-lined baking sheet. Distribute the cooled compote evenly between the 8 tarts. Fold in about an inch of dough all the way around; brush the edge lightly with milk and sprinkle the edge with sugar. Bake crostatas for 40-50 minutes or until the crust is golden brown and the filling inside is bubbling. Serve with whipped cream, ice cream or custard.