Roasted Pumpkin Soup With Brown Butter and Thyme

1 lemon, juice from

Bay leaves

Leeks, large

Sugar pumpkins or kabocha squash, medium

Thyme, whole stems

Yellow onion, finely sliced (about 3/4 cup), small

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

Maple syrup

Kosher salt and freshly ground black pepper

Olive oil, extra-virgin

Butter, unsalted