Assemble ingredients and tools. Preheat the oven to 400 degrees.
Remove the feathery tops from the fennel bulb, and chop the bulb into pieces.
Steam or microwave the chopped fennel until tender.
Scrub and slice the potatoes. Slice the summer squash into rings. Chop the fresh herbs.
Butter a heavy, gratin or cast iron pan well and layer the cooked fennel in the bottom of the pan.
Layer the sliced summer squash on top of the fennel. Season the squash with salt and pepper. Layer the potato slices over the summer veggies. Season the potatoes layers with salt and pepper and dot with butter.
When the casserole is complete, dot the top with the remaining butter. Sprinkle with the fresh herbs and grated cheese. Pour the cream over the top and bake until the potatoes are fork-tender and the top is golden, about 30-40 minutes.