Step 1

Place racks in upper and lower thirds of oven and preheat to 425°. Toss eggplant, fennel seeds, red pepper flakes, 6 Tbsp. oil, and 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt in a 3-qt. or 13x9" baking dish; season with black pepper. Roast on bottom rack, tossing halfway through, until golden and tender, 25–30 minutes. Let cool.

Step 2

Meanwhile, heat remaining 1 Tbsp. oil in a large Dutch oven or other heavy pot over medium-high. Add haricots verts, season with salt, and cook, tossing every minute or so, until they start to release moisture and steam, about 5 minutes. Add anchovies, garlic, wine, and tomato paste and cook, stirring with a wooden spoon or heatproof rubber spatula to break up paste, 1 minute. Add ¾ cup water, cover pot, and cook until haricots verts are crisp-tender, 5–7 minutes.

Step 3

Add cherry tomatoes and butter beans, re-cover pot, and cook until tomatoes start to burst, 5–7 minutes. Remove pot from heat, uncover, and stir in parsley, marjoram, and thyme.

Step 4

While the beans and tomatoes are cooking, spread Gruyère out on a parchment-lined baking sheet and bake on top rack until melted and almost done bubbling and golden, 8–10 minutes (check often). Let cool.

Step 5

Using a slotted spoon, scoop tomato and bean mixture over and around eggplant in baking dish, arranging so everything is nestled together but eggplant isn’t completely covered. Pour liquid left in pot over. Remove crispy Gruyère from parchment and crumble on top of cassoulet.