1. Place the chopped pumpkin, broccoli florets, and finely chopped beef into a medium-sized saucepan.
2. Add 500 ml of water to the saucepan.
3. Bring the mixture to a boil over medium heat.
4. Once boiling, reduce the heat to low, cover the saucepan, and simmer for 20 minutes until all ingredients are tender.
5. Remove the saucepan from heat and allow the mixture to cool slightly.
6. Transfer the cooled mixture to a blender or food processor.
7. Blend the mixture until you achieve a smooth puree consistency. You can add a little more water if needed to reach the desired texture.
8. Allow the puree to cool to a suitable temperature before feeding it to your baby.

Summary:
This Pumpkin, Broccoli, and Beef Baby Puree is packed with essential nutrients like vitamins, minerals, and proteins that are excellent for your baby's growth and development. Pumpkin provides a good source of Vitamin A, broccoli is rich in Vitamin C and fiber, while beef offers necessary protein and iron.

Storing Options:
You can store any leftover puree in an airtight container in the refrigerator for up to 3 days or freeze it in small portions for up to 1 month.

Possible Side Effects/Allergies:
Always watch for any signs of allergies or sensitivities, particularly when introducing new foods. Common signs include rashes, swelling, or gastrointestinal discomfort. Consult with a pediatrician if you have any concerns or questions about your baby's diet.