4. Sauté Onions and Apples
To the empty sauté pan, add the sliced onions and apples. Season with salt and pepper and cook, stirring occasionally, until the onions and apples are just starting to soften, about 5 minutes. If at any time the onions and apples get too dark before they start to soften, reduce the heat slightly.
Add the garlic and cook, stirring constantly, until softened, about 1 minute. Stir in the mustard and pepper flakes and remove
from the heat.