Preheat your oven to 400°F (200°C).
Wash, peel, and remove the seeds from the butternut squash. Cut into approximately 1/2-inch cubes.Place 2 1/2 cups of cubed squash on a baking sheet with the fresh thyme. Drizzle with olive oil and toss until evenly coated. Roast for 25–30 minutes, stirring halfway through, until the edges are lightly golden and the squash is very soft and easily mashed with a fork.
Allow the squash to cool slightly, then transfer it to a blender or food processor.Add 1/4 cup of water and blend until smooth, adding more liquid a little at a time if needed. Prepared infant formula or breast milk can be used instead of water once the squash has cooled. Allow the puree to reach a safe serving temperature and check that the texture is appropriate for your baby's developmental stage.