1. In a bowl, beat together the eggs, milk and butter until the mixture is combined well.
2. Add the flour and salt and beat the mixture until just combined. (The batter will be slightly lumpy.)
3. Divide the batter among 9 very generously buttered 1/2-cup muffin tins or six 2/3-cup popover tins. Bake in the middle of a 375° F. oven for 1 hour.
4. Cut a slit in the top of each popover with a small sharp knife and bake the popovers for 10 minutes more. Serve with the jam.