Step 1

Preparation Preheat oven to 400°F. Place beets in small baking dish. Add enough water to reach depth of 1/4 inch. Sprinkle lightly with salt and pepper. Cover tightly with foil. Bake until beets are tender, about 50 minutes. Uncover carefully (steam will be released) and cool. Peel beets; cut into 1/4-inch-thick slices. DO AHEAD: Can be made 2 days ahead. Cover and chill.

Step 2

Preheat oven to 425°F. Bring cream, mint sprigs, and garlic to boil in heavy small saucepan. Remove from heat, cover, and let steep 15 minutes.

Step 3

Meanwhile, lightly butter 1 1/2-quart gratin dish or other shallow baking dish. Arrange sliced beets in even layers in dish, sprinkling each layer lightly with salt. Strain cream mixture over beets in dish. Sprinkle feta over. Bake until cream is bubbling at edges and feta is browned in spots, about 20 minutes. Sprinkle pepper and chopped mint over. Let stand 5 minutes before serving.