1. Begin by preparing the chicken. Rinse the chicken breast under cold running water and then cut it into smaller pieces for even cooking.
2. In a medium-sized pot, add the chicken pieces and enough water (or low-sodium chicken broth) to cover the chicken completely. Bring to a boil over medium heat.
3. Once boiling, reduce the heat and let it simmer for about 10-15 minutes until the chicken is cooked through (the internal temperature should reach 75°C).
4. While the chicken is cooking, prepare the butternut squash. Place the diced squash in a separate pot of boiling water and cook for approximately 10-15 minutes, or until tender.
5. Once both the chicken and squash are cooked, drain the squash and set aside.
6. Add the cooked chicken and butternut squash to a blender or food processor. Pour in a little of the cooking liquid (about 100 ml) to help with blending.
7. Blend the mixture until smooth, adding more liquid if necessary to achieve the desired consistency.
8. Allow the puree to cool slightly before serving.

Summary:
This Chicken and Squash Puree is a nutritious meal for babies aged 4-10 months. Chicken provides essential protein and nutrients for growth, while butternut squash offers vitamins and fiber. The smooth texture makes it easy for babies to consume.

Storing Options:
The puree can be stored in an airtight container in the refrigerator for up to 3 days or frozen for up to 3 months.

Possible Side Effects/Allergies:
As with any new food, introduce it gradually and watch for any potential allergies, particularly to chicken or squash.