Honey-Rosemary Grilled Pork and Beets

3 medium beets
1 pork tenderloin (about 1 pound)
6 tablespoons honey, divided use
3 tablespoons chopped fresh rosemary
2 tablespoons butter

Preheat grill to medium. Lay out 6 sheets of aluminum foil, each about 10 by 12 inches. Wash beets and cut each into 4 slices. Divide beets among 4 foil sheets. Cut pork in half crosswise; put each half on its own foil sheet. Combine honey and rosemary in a small, microwave-safe bowl. Spoon 2 teaspoons of the mixture over each pork half and each sheet of beets. Fold foil to make packets, sealing tightly but allowing some room for air to circulate. Grill packets 25 minutes, turning once. Remove from heat and let packets rest 5 minutes before opening. Meanwhile, add butter to bowl with remaining honey and rosemary. Microwave 15 seconds; stir until blended. Open packets and cut each pork half into 2 pieces. Divide pork and beets among 4 dinner plates. Drizzle with butter sauce.