How to seal a terrine or casserole dish (Slideshow version)
The French have a term for it: "luter", which means to seal around the lid of a cooking dish with dough.
The dough forms a crust and hermetically seals in all the steam and flavours while the dish is cooking in the oven.
This is a good way to concentrate flavours. The dish is brought to the table sealed and the crust broken open in front of diners so that everyone can share the delicious smells as they are released at that fleeting moment.
It is possible to use ordinary bread dough, but an unleavened (or "dead") dough, with neither natural leaven nor yeast will work better.