Beet Gratin with Goat Cheese and Greens

Name: Beet Gratin with Goat Cheese and Greens
Ingredients: 3 pounds red beets (about 6 medium beets), with greens attached; Salt and freshly ground black pepper; Olive oil; 2 cloves garlic, minced; 2 ounces goat cheese, finely crumbled; 1/2 cup whole milk; 1 cup dry bread crumbs; Zest of 1 lemon; 4 sprigs fresh thyme (leaves only)