Lidded Dish With Glass Insert

Is this glass piece original to the dish? Is so, what’s its purpose?

 

What are the diameters of the bottom silver piece and the glass piece?

 

Having realized from the picture of the glass piece resting on your had that that piece is relatively small, I'd guess that the glass part holds whatever needs to remain cold while ice under the glass sends cold air up through the hole. Butter, most likely. But could also be shrimp or anything else.

 

Thanks. Very likely a butter dish but would never guess the glass part. Do you think it came like that or someone’s clever idea?

 

If it fits properly, I'd say original.

 

Thanks. The glass insert is exact fit.