For the sauce, combine miso and sugar in a medium-size, heavy-bottomed saucepan. Whisk in sake and mirin. Over low heat, bring to a simmer and cook, frequently stirring, until sugar dissolves, color darkens, and it has the consistency of a thick sauce—approximately 45 minutes. Sauce can be made up to a day in advance and should be refrigerated. When ready to use, reheat in a pan on low heat for 2–3 minutes.

Preheat oven to 425°F.

Cook bacon in a small skillet over medium heat, stirring often, until crisp, about 5 minutes. Remove from heat and set aside.

Cut eggplants in half lengthwise. Use the tip of a paring knife to score cut sides in a crosshatch pattern. Brush scored sides with olive oil, then spread 1 teaspoon of miso mixture over each half. Place on parchment-lined baking sheet. Roast eggplant for about 20 minutes, until tender and browned.

Sprinkle with sesame seeds, chives, and bacon, and serve.