We found our clear glass egg coddlers work well to store, heat and serve tiny portions of homemade baby food. Just pop them in a pan of hot water with mashed veggies instead of an egg. Ours are tempered glass that can go easily from freezer to stove to table to dishwasher, and are a little more elegant than re-used glass baby food jars.
Unfortunately, I can't seem to find widely-available glass egg coddlers; just the porcelain ones pictured here. Williams-Sonoma also sells a porcelain version.
Related: How to make baby food