Aged Cheddar, Smoked Ham, and Apple Galette

1 T. salted butter

2 T. all-purpose flour

¾ cups milk

2 T. grainy mustard

2 cups grated aged cheddar cheese

1 cup (1-inch) cubed smoked ham

2–3 large baking apples, cored, cut into ¼-inch slices (peel left on)

1 tsp. grated lemon zest

Flaked sea salt and cracked black pepper

1½ cups all-purpose flour

2 T. thyme leaves

½ tsp. fine sea salt

½ cup cold unsalted butter, cut into 1-inch cubes

5–6 T. cold water

1 large egg

1 T. milk

 

To make the pastry, place the flour, thyme, and salt in a food processor. Pulse once to combine. Add all the butter and pulse a few more times until the mixture is crumbly and the butter is cut down into pea-sized pieces. Add the cold water, 1 Tbsp at a time, pulsing in between to bring the dough together. Dump the dough out onto a piece of plastic wrap and form it into a disc. Wrap it tightly and refrigerate for at least 30 minutes. Preheat the oven to 425°F. Line a rimmed baking sheet with parchment paper. To make the filling, first melt the butter in a saucepan over medium heat and add the flour. Stir to combine and cook until the flour begins to brown and has a slightly nutty aroma. While whisking constantly, add the milk and continue to stir until the roux thickens. Remove from the heat and add the grainy mustard. Set aside.  In a large bowl, place the cheese, ham, apple slices, lemon zest, and a pinch of salt and pepper. Toss lightly just to combine. Place the dough on a well-floured work surface and roll it into a 12-inch circle. Transfer the dough to the prepared baking sheet. Spread the mustard roux over the middle of the pastry, leaving a 2-inch-wide border along the perimeter. Top with the cheese, ham, and apple mixture. Fold the bare edges of the dough in towards the centre to form a rustic crust. Make an egg wash by beating the egg with the milk. Brush the crust with the egg wash and bake the galette for 25–30 minutes, or until the crust is golden brown and the filling is bubbling. Remove the galette from the oven and allow to cool in the pan for 5–10 minutes before serving