Season the chicken cutlets with salt and pepper on both sides.
In a large skillet, turn the heat to medium and add the chopped bacon. Let the fat render out until the bacon is crisp, then remove the bacon with a slotted spoon to a paper towel to drain.
Add the rosemary to the skillet and fry for 30 seconds to release the flavors.
Add the chicken cutlets in a single layer directly in the bacon fat, and cook for approximately 3 minutes on each side (this time varies with thickness). The exterior of the chicken should develop a little bit of golden brown color as it cooks. If it's not browning, increase the stove setting to medium-high heat.
Once the chicken has completely cooked to 165F, remove the cutlets to a plate, and deglaze the pan with the Brandy, if using, and the chicken stock.
Cook for a few minutes until the liquid mostly evaporates, then add the mustard and cream.
Turn the heat to high and whisk, incorporating the brown bits from the bottom of the pan into the sauce.
Cook the sauce for a couple minutes, until the cream has thickened slightly, then turn off the heat and add the chicken and bacon bits back to the pan.
Turn the chicken over in the sauce a few times to coat, then serve.