Combine flour and salt in a food processor and pulse to combine. Cut the cold butter into small cubes and add to the flour, pulsing until the mixture resembles coarse breadcrumbs with some pea-sized butter pieces remaining—this creates a flaky texture. In a separate bowl, whisk together yogurt, cold water, and lemon juice. Pour the wet mixture into the flour and pulse just until a shaggy dough forms; don't overmix. Transfer to a floured surface, gently bring it together into a disk, wrap in plastic, and freeze for at least 20 minutes while you prepare the filling.

While the dough freezes, trim the asparagus to 4-inch lengths and set aside. Mince the garlic clove and whisk it together with olive oil in a small bowl, letting the garlic infuse slightly. In another bowl, combine the goat cheese, freshly grated Parmesan, and mozzarella, then toss with 1 teaspoon of the garlic-oil mixture—I find this distributes the flavor evenly throughout the cheese. Season the asparagus lightly with black pepper and set aside. Preheat your oven to 400°F.

Remove the chilled dough from the freezer and place on a floured surface. Roll it out into a rough 12-inch circle, about 1/8-inch thick—it doesn't need to be perfect, as the rustic shape is part of the charm. Transfer to a parchment-lined baking sheet. Spread the cheese mixture from Step 2 evenly over the dough, leaving a 2-inch border all around. Arrange the trimmed asparagus spears over the cheese in a single layer or slightly overlapping pattern. Drizzle the remaining garlic-oil mixture over the asparagus.

Fold the 2-inch dough border up and over the filling, creating rustic pleats as you go—the center will remain exposed, showing off your beautiful asparagus. Whisk together the egg yolk with 1 teaspoon of water to create an egg wash, then brush it generously over the folded crust edges. This gives the pastry a beautiful golden-brown finish. Bake at 400°F for 30 minutes until the crust is golden and the cheese is melted and bubbling at the edges. Let cool for 5 minutes before slicing and serving—I like to let it set slightly so the filling doesn't run when you cut into it.