Preheat the oven to 375°.
Melt 1 tablespoon of butter (I like to use the microwave), and add to a large bowl. Add the pound cake to the bowl and toss to coat all the cubes with the butter. Spread the cubes on a baking sheet and bake for about 10-15 minutes, until toasted.
Add the remaining 3 tablespoons of butter and the nectarines to a skillet and cook over high heat, stirring occasionally, until the nectarines are slightly softened, about 5 minutes.
Add the brown sugar and stir to melt into the nectarines.
Remove the skillet from the heat, then add the bourbon and lemon juice. Tilt the pan slightly and carefully ignite the alcohol. Cook over moderate heat until the nectarines are softened and the sauce is slightly thickened, about 10 minutes. **If you’re concerned about the whole “adding the alcohol and lighting it on fire” just continue simmering until the liquid reduces and thickens up a bit.
Scoop the ice cream into bowls and spoon the nectarines and sauce on top.
Garnish with the croutons and serve right away.
**If you want to make the nectarines and pound cake croutons ahead of time, you can make them earlier in the day and store in the refrigerator. Warm up the nectarine mixture before assembling the dessert.