Completely butterfly each of the chicken breasts, making a total of 4 thin chicken breasts. One by one, put the chicken breast in between 2 pieces of plastic wrap and flatten slightly with a mallet.

Put the pretzels in a food processor and process until you have fine crumbs. Put the crumbs in a shallow dish and season with salt and pepper. In another shallow dish, beat the eggs.

In a large saute pan over medium heat, heat up the oil, about 1/8″ deep.

Dip each chicken piece into the pretzels, then into the eggs, then back into the pretzels. Add to the hot oil in the pan. Put the chicken into the hot oil and cook until the pretzels are browned and the chicken is cooked through. This only takes about 3 or 4 minutes on each side.

Meanwhile, make the sauce. In a saucepan, melt the butter. Whisk in the flour and cook for 1 minute. Whisk in the milk and the mustard, and cook until slightly thickened. Stir in the cheese. Season with salt and pepper, if needed.