Chop the kabocha squash into bite-sizes, then remove the seeds, pith, and skin. Layer a microwave-safe dish with a paper towel. Place the kabocha onto the paper towel, then microwave. (Use the setting for root vegetables, if available.) Take them out once they are tender enough for skewer to be easily inserted.

Mash the kabocha with a mortar and pestle until smooth. If you prefer a creamy texture, pass it through a strainer to make a purée.

Melt butter in a pan, add the mashed kabocha, then, adding a little milk at a time to dilute, stir with a wooden spatula, taking care not to burn it. When the batter reaches an even consistency that smoothly slides off of the spatula, add sugar a little at a time. Add cinnamon to taste, then remove from heat.

Slice the banana. Pour 1/2 of the batter from Step 3 into a casserole dish, layer with banana slices, then pour the rest of the batter on top, covering the banana entirely. Smooth out the surface, then sprinkle cinnamon.

Bake for about 10 minutes at 390F/200℃. When the surface browns to a nice finish, it's finished baking. Allow it to cool down, then chill it in the refrigerator.

Scoop onto individual dishes with a spoon. Whip heavy cream and a little sugar to a thin yoghurt-like consistency, then add a dollop on top of each serving. Bon appetit!