In a large bowl whisk together 2.25 cups flour, 0.5 tsp salt and 1 tsp sugar. Add 0.5 cup cold cubed unsalted butter. Using a pastry cutter or fingertips, cut the butter into the flour until mixture resembles coarse crumbs with some pea-sized pieces remaining.

Add water and chill

Sprinkle 6 tablespoons cold water over the flour mixture, one tablespoon at a time, tossing gently until dough just comes together when pressed. Do not overwork. Form dough into a disk, wrap tightly in plastic, and chill in refrigerator for at least 30 minutes (up to 2 hours).

Roll out

When ready, lightly flour a work surface and roll chilled dough into a roughly 12 x 10-inch rectangle about 1/8 inch thick. If making individual pastels instead of one large pie, divide dough into 6 equal pieces and roll each into 6-inch rounds. Transfer rolled dough to a baking sheet lined with parchment if assembling there, or set aside on lightly floured surface covered with plastic to keep from drying.

Filling

Cook aromatics and vegetables

Heat 1 tablespoon olive oil in a large skillet over medium heat. Add 1 cup finely diced onion and cook until softened and translucent, about 4–5 minutes. Add 0.5 cup diced carrot and 0.5 cup diced bell pepper and cook another 4 minutes until vegetables begin to soften. Stir in 1 teaspoon minced garlic and cook 30 seconds until fragrant.

Add ham and peas

Add 2 cups diced ham and 0.5 cup thawed peas to the skillet. Cook 2–3 minutes until ham is warmed and peas are heated through.

Make sauce

Sprinkle 2 tablespoons flour over the mixture and stir to coat; cook 1 minute to remove raw flour taste. Stir in 3 tablespoons milk, 1/2 cup chicken or vegetable broth, and 1 teaspoon Dijon mustard, stirring constantly until the sauce begins to thicken, about 2–3 minutes. Add 0.5 teaspoon dried thyme, 0.75 teaspoon salt and 0.5 teaspoon black pepper. Remove from heat and stir in 0.5 cup grated cheddar if using. Taste and adjust seasoning.

Cool filling

Transfer filling to a bowl and let cool for 10–15 minutes so it firms slightly (this prevents soggy pastry). If making individual pastels, divide filling into 6 equal portions.

Assembly & Bake

Preheat oven

Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease.

Fill pastels

If using one large rectangular pastel: transfer rolled dough to the prepared baking sheet. Spoon the cooled filling down the center third of the rectangle in a log, leaving a 1-inch border on all sides. Optionally fold in edges and then fold dough over the filling to enclose, pressing seams to seal and tucking ends. For individual pastels: place a portion of filling in the center of each 6-inch round, brush the edge with a little water, fold into half-moons and press edges with a fork to seal. Make a few small slits in the top of each pastel to vent steam.

Egg wash and finish

Whisk together 1 large egg and 1 teaspoon water to make an egg wash. Brush the top and edges of the pastry lightly with the egg wash. Sprinkle 0.25 tsp coarse sea salt or sesame seeds on top if desired.

Bake

Bake in the preheated oven for 20–25 minutes for individual pastels or 30–35 minutes for a single large pastel, until pastry is golden brown and filling is bubbling near vents. Rotate the baking sheet halfway through for even browning.

Rest and serve

Remove from oven and let rest 5–10 minutes before slicing or serving to allow filling to set. Serve warm or at room temperature.