White and Green Asparagus Gratin

1 c. heavy cream
2 shallots, minced
2 sprigs fresh thyme, bundled together
¼ c. dry white wine
Salt and freshly ground black pepper
½ bunch green asparagus; trimmed and cut diagonally into ½-inch slices
½ bunch white asparagus; trimmed, peeled, and cut diagonally into ½-inch slices
1⅛ c. grated Parmesan cheese
¼ c. panko bread crumbs
2 Tbsp. melted butter

Preheat the oven to 400°. In a medium saucepan, combine the cream, shallots, thyme, and wine; place over medium heat and simmer until reduced by half, 20 to 30 minutes. Discard the thyme bundle and season the cream mixture with salt and pepper.
In a large mixing bowl, combine the asparagus, reduced cream, and 1 cup of the Parmesan cheese; mix well and place in two individual (approximately 16 ounce) gratin dishes, or other equal-sized ovenproof baking dish. Sprinkle the remaining Parmesan over the tops of the asparagus. In a small mixing bowl, combine the panko bread crumbs and melted butter; sprinkle the bread crumbs on top of the dishes. Place the gratin dishes on a baking sheet, set in the oven, and bake until the asparagus are tender, the sauce is bubbling, and the bread crumbs are golden brown, 6 to 10 minutes. Serve hot.