Step 1

Pulse butter, 3 cups flour, and ½ tsp. salt in a food processor until mixture resembles coarse meal with a few pea-size pieces of butter remaining. With motor running, stream in ½ cup ice water and process, adding more water by the tablespoonful if needed, until a shaggy dough comes together and starts to form a ball around the blade (a few dry spots are okay).

Step 2

Transfer mixture to a lightly floured surface and gently knead until dough comes together completely (don’t overmix). Divide dough in half, flatten each piece into a ½"-thick square, and wrap in plastic. Chill until cold, at least 2 hours.

Step 3

Meanwhile, cook peas in a medium saucepan of boiling salted water until bright green, about 30 seconds. Drain and transfer to a bowl of ice water to cool. Drain and pat dry.

Step 4

Blend oil and 1 cup peas in a food processor until smooth; season pea purée with salt and pepper.

Step 5

Mix ricotta and lemon juice in a small bowl; season with salt. Whisk egg and vinegar in another small bowl.

Step 6

Preheat oven to 375°. Let dough sit at room temperature, about 5 minutes, to soften slightly, making it easier to roll. Working with 1 square at a time, roll out dough on a lightly floured surface to about a 13x11" rectangle. Trim to 12x10", then cut into eight 5x3" rectangles. (A ruler in the kitchen is a useful thing, but if you’re not that particular, eyeball it.)

Step 7

Arrange 8 rectangles on a parchment-lined rimmed baking sheet, spacing 2" apart. Spread 1 Tbsp. ricotta mixture over each, leaving a ½" border, then spread a dollop of pea purée over ricotta. Top with ham and remaining whole peas.

Step 8

Brush borders with egg wash and top with remaining 8 rectangles of dough, pressing gently around edges to seal. Crimp with a fork. Brush tops of tarts with egg wash and make 3 slits in the center of each (for steam to escape). Sprinkle with salt and pepper and bake, rotating halfway through, until tarts are deep golden brown, 35−40 minutes. Transfer to a wire rack and let cool 15 minutes.

Step 9

Do Ahead: Dough can be made 3 days ahead; keep chilled. Hand pies (without egg wash) can be formed 1 day ahead; cover and chill. Brush with egg wash just before baking.