Roasted Cauliflower Soup With Bacon and Parsley Oil

slices Bacon

medium heads Cauliflower

Parsley, fresh leaves

White or yellow onion, peeled and finely chopped (about 1 1/2 cups), large

Vegetable or chicken stock, homemade or store-bought low-sodium

Kosher salt and freshly ground black pepper

Olive oil, extra-virgin

Half and half