In a stand mixer fitted with a paddle attachment, combine the flour, sugar and salt. Cut the butter into ½-inch cubes and add them to the flour. On low speed combine the butter and flour just until the flour is no longer white and holds together when you clump it with your fingers — 1 to 2 minutes. If there are any lumps of butter larger than a pea, break them up with your fingers.
In a small bowl, mix the egg yolk and milk, then add to the flour mixture (on low speed… about 15 seconds). The dough ought to still be a little lumpy and perhaps dry. Dump it onto a clean and lightly floured work surface. Work it with the heel of your hand, pushing and smearing any clumps of butter away from you, then gathering it back together with a bench scraper, until the dough comes together. Wrap the dough in plastic wrap, then flatten it into a flat disk and refrigerate for at least a half hour (up to four days — you can freeze it for months and months).
Heat oven to 350 degrees.
On a floured surface, roll out the dough into a 13 to 14 inch-round — it’s okay if the edges are a little ragged. Place on a baking sheet and stick it back in the fridge while you get the fruit together.
For the filling, you’ll need about 4 cups of fruit total. Combine the fruits, sugar, cornstarch and extract (if using).
If using almond paste, form about 4 to 5 tablespoons into a ball; flatten the ball, then roll out into a thin circle.
Remove the pastry from the fridge and let it sit for a few minutes. Place the almond paste disk in the center (it’s okay if it tears — you can even break it up into pieces). Heap the fruit in the center of the dough leaving a 2-inch rim around the outside (or carefully arrange it in a circular pattern if you are using sliced stone fruit or apples). Fold the edges of the dough over the fruit, pleating as you go.
If you are feeling fancy, you can make an egg wash and brush the exposed dough, then sprinkle it with sugar. Bake for 50-55 minutes, or until the pastry is light brown and juices are starting to run.