I have a bug somewhere in a UDF I wrote. I put some breakpoints in the
code, but it's called from 30-40 cells in the worksheet. Is there a
way to get Excel to recalculate just one cell so I don't have to keep
setting and resetting the breakpoints or hit F5 30-40 times until all
of the other cells finish?

In the past, I've just pressed F2 on the cell in question and I
thought it only re-executed that one cell. Today it is recalculating
the entire sheet and, sometimes, the entire workbook.