What it is and where it comes from
E476 is made from the fatty acids of castor oil, a plant, joined to polyglycerol. The polyglycerol is made from glycerol, which is usually from plant oils but can come from animal fat. That small chance is why it is not marked halal outright.
Where you find it
Chocolate and chocolate coatings, where it helps the chocolate flow, and low-fat spreads.
What to look for on the label
Chocolate with a halal logo, or labelled vegan, is fine. For other chocolate, the maker can confirm that the glycerol is from plants.
This is a guide, not a fatwa. Recipes change, so check the label, look for halal certification, and ask your local imam where scholars differ.