Step 1: Prepare the Crust
The crust is a crucial part of any tart—it should be buttery, flaky, and golden brown. Here’s how to do it:

1. Start by placing the flour and salt in a food processor. Add the cold, cubed butter and pulse until the mixture looks like coarse crumbs (about 15-20 pulses).
2. Add the egg yolk and pulse a few more times. Then, add the cold water, one tablespoon at a time, pulsing until the dough just starts to come together.
3. Turn the dough out onto a lightly floured surface and knead it a few times to bring it together. Wrap it in plastic wrap and refrigerate for at least 30 minutes.

Step 2: Roast the Brussels Sprouts
While the dough chills, roast the Brussels sprouts to bring out their natural sweetness and depth of flavor. Here’s how:

1. Preheat your oven to 400°F (200°C).
2. Toss the Brussels sprouts with olive oil, salt, and pepper on a baking sheet. Roast for 20-25 minutes, stirring halfway through, until they are crispy on the edges and tender on the inside.
3. Remove from the oven and set aside to cool slightly.

Step 3: Roll Out the Dough
Once your dough has chilled and the Brussels sprouts are roasted, it’s time to assemble the tart.

1. On a lightly floured surface, roll the dough out into a circle about 12 inches in diameter.
2. Transfer the dough into a 9-inch tart pan, pressing it into the bottom and up the sides. Trim any excess dough around the edges.
3. Place the tart crust in the fridge while you prepare the filling.

Step 4: Make the Filling

1. In a large mixing bowl, whisk together the heavy cream, eggs, salt, pepper, and nutmeg until smooth.
2. Stir in the minced garlic and fresh thyme leaves.
3. Gently fold in the roasted Brussels sprouts and chopped pistachios, making sure everything is well combined.

Step 5: Assemble the Tart

1. Preheat your oven to 375°F (190°C).
2. Pour the filling into the prepared tart crust, spreading it out evenly with a spatula.
3. Sprinkle the grated Parmesan cheese evenly over the top.
4. Place the tart in the oven and bake for 30-35 minutes, or until the filling is set and the top is golden brown.
5. Let the tart cool for 10-15 minutes before removing it from the pan.