Simply increase the portion sizes of nutritionally dense foods that you are already eating. If you are losing weight at 1,700 kCal/day then increase the amount you eat to 2,000 kCal/day and so on until your weight stabilizes. If meal sizes get uncomfortably large, add a few snacks throughout the day. Nuts and nut butters, dates, figs, bananas, granola (watch the quality as some borders on junk food), hummus, and many other nutritious foods are fairly calorie dense while still providing vitamins, minerals and fiber.