Turn oven to lowest setting.

Split and toast muffins.

Spray nonstick skillet with cooking spray and set over high heat. Fry bacon just until it begins to brown, about 1 minute on each side.

Remove bacon from skillet and drain.

Arrange toasted muffin halves on baking sheet or heat-proof serving platter and place a bacon slice on each half. Place in oven to keep warm.

Wipe out skillet and place on low heat. Add butter to melt.

Add onion slices and saute 3 minutes.

Add apple slices to skillet. Sprinkle with granulated sugar and raise heat to med-high. Cook until apples and onions are tender, about 5 minutes.

Scatter apples and onions evenly over the bacon-topped muffins. Return to oven to keep warm.

Whisk together half-and-half, brown sugar and mustard.

Pour this into same skillet and bring almost to a boil over medium heat, whisking constantly. Cook for 1 minute more, but don't let boil.

Transfer 2 muffin halves to each individual serving plate, topping with plenty of apples and onions. Top with sauce and serve immediately.