Score chestnuts and place in boiling water for 5 minutes till tender. Peel to remove both skin and fine inner pellicle as soon as they're cool enough to handle. They'll peel better warm.
Peel and deseed pumpkin and cut into 2cm cubes.
Place in a baking dish with peeled chestnuts and sage, toss with olive oil, salt and pepper.
Place in a preheated 180C oven for 30 minutes. Remove from oven and let cool.
Slice each chestnut into 5-6 slices.
Plate by stacking cubes of pumpkin in a pile on each plate, spoon ricotta around and scatter the sliced chestnuts on top.
Use the sage leaves as garnish and any pan juices over the top as dressing. Finish by sprinkling sesame seeds over.