I have begun with a humble sweet potato. I love them, and babies love them. My husband loves them too, although he never knew it before marrying me. (His dad hated them so his mom never served them. Our eating habits rub off on our children--let that be a lesson to you!)
I peeled it, sliced it in half, and cubed it. It's a good idea to make the cubes similar in size so that they cook evenly.
I prefer to steam my vegetables. This leaves more nutrients in the veggies than boiling would. I also think steaming increases the water content a little bit helping to make a nice soft puree.
If you've never steamed anything before here's a primer: Open your drawer of random kitchen doodads. Find that weird holey metal thing that opens up like a lotus blossom--you know the one--it's called a steamer basket. It's made to expand to fit almost any sized pot, so pick one of yours and put about 3/4 of an inch of water in the bottom and put the steamer basket inside. Put the lid on the pot and get the water boiling. Then put your vegetables in, replace the lid, and steam the veggies until they offer little resistance to a fork or knife. (If it is taking a while for your vegetables to steam you may need to add more boiling water, or turn the heat down to a lower boil. I have boiled all my water away before and it's no good for your pots, and it leaves your house smelling terrible!!!)
Transfer the vegetables to a food processor and puree! If you don't wait for them to cool then you should leave the rammer/stomper/whatever thing out of the lid so that steam can escape. If the puree is not thin enough for your baby's needs you can add some of the water left over from steaming (Otherwise you can use it in a soup).
Spoon the puree into an ice cube tray. Cover with plastic wrap and put in your freezer.
When the cubes are frozen pop them out of the tray and place them in a freezer bag or container. The little one-ounce portions are perfect. I would put one in a little Tupperware bowl and throw it in the diaper bag. Just as easy as a jar! This is one of the little things I like to do to help "offset the cost" of being a stay-at-home mom:-)