Why do we call wealthy members of society “the upper crust”?

In the days of feudalism, when noblemen gathered for a meal in the
castle, those of higher rank sat at the head of a T-shaped table, and the
rest sat in order of diminishing importance away from them. For such
occasions a yard-long loaf of bread was baked, and the honour of mak-
ing the first cut belonged to the highest-ranking person at the head
table, who would then pass the bread down in order of rank, but always
keeping for himself the “upper crust.”