I'm going to talk about how to incorporate breast milk or formula into your baby's baby food purees. It's actually a great thing to incorporate because both breast milk and formula are nutrient dense, great source of iron, vitamins, minerals, and they're also really great for thinning down thicker purees. So this puree's a little thick, you could very easily add teaspoon by teaspoon either breast milk or formula and thin it down until you get to the consistency that your baby prefers. It's also great to use in place of water when you're preparing baby cereals.
So quinoa cereal, buckwheat cereal, oat cereal, you can easily use breast milk or formula in place of the water and then your baby ends up with a much more nutrient dense meal.
One precaution you should take with using breast milk or formula in your baby's food is not to save it in the refrigerator or freezer. Formula tends to go bad quite quickly and there's a very high risk of bacterial growth if you save it in the fridge or freezer and then reheat it and serve it to your baby later. So that is the only thing you do not want to do with formula or breast milk.