Toast Puzzle

I don't have a toaster, but my pan can hold three slices of bread when I make toast.

Each slice has to be toasted on both sides, of course, and it takes one minute to toast a side, including "turning over time".

I can therefore make three slices of toast in two minutes. How long would it take for four slices?

I thought that it would take me an extra two minutes for a total of four minutes to make four slices, until my friend Hungry Horace said I could do it in just three minutes. How is it done?