Prepare butternut squash: Preheat the oven to 180 degrees Celsius. Peel and cut the butternut squash into 2cm cubes.
Cook the squash: Melt the butter over medium heat in a non-stick pan. Add the onions and stir for one minute. Add the garlic and sauté for 30 seconds. Stir in the butternut squash until all the pieces are coated in the butter. Cook covered for 15 minutes, adding a little water if it is too dry.
Add the Thyme: Add the thyme leaves, season and cook for another 5 minutes until soft.
Mash the squash: Roughly mash the butternut squash and add the cream and some of the cheese, stirring well. Cook for another 2 minutes.
Bake the squash: Transfer the cooked butternut squash into a gratin dish. Top with cheese and sprinkle the breadcrumbs. Bake in the oven for 15-20 minutes until golden brown. Enjoy piping hot!