Preheat your oven to 400°F (200°C). Roll out the thawed puff pastry onto a lightly floured surface into a 10x14-inch rectangle. Lightly score a 1-inch border around the edges and prick the center with a fork to prevent puffing. Transfer to a parchment-lined baking sheet and bake for 12-15 minutes until golden.

In a mixing bowl, whisk together 2 large eggs, 1 cup Greek yogurt, 2 minced garlic cloves, 1 teaspoon salt, and 6 ounces shredded sharp white cheddar cheese until smooth. Spread this creamy filling into the center of the cooled puff pastry crust.

In a skillet, melt 2 teaspoons of butter over medium heat. Add ½ pound of asparagus and sauté for about 2 minutes. Then, add 1 cup of diced lean ham and cook for an additional 2 minutes until browned.

Scatter the sautéed asparagus and ham mixture over the creamy filling in the puff pastry. Brush the exposed edges of the crust with the beaten medium egg.

Return the assembled tart to the oven and bake for 10-12 minutes until the filling is set and the crust is golden. Sprinkle fresh thyme leaves on top before serving.