Halve each chicken breast lengthwise to create 4 even-sized pieces.
Whisk together the flour, salt, and pepper in a shallow bowl. Dredge both sides of the chicken in the flour mixture. Set aside.
Melt 2 tablespoons butter in a large skillet over medium-high heat. Add in the chicken and sear on both sides until golden. Remove from the pan and set aside.
Add in the remaining butter, shallot, and rosemary. Sautee until the shallots soften.
Add in the wine, and cook until evaporated, scraping the brown bits from the bottom of the pan.
Add in the chicken broth, mustard, heavy cream, salt and pepper.
Stir to combine and simmer for 2-3 minutes until the sauce slightly thickens. Add the chicken back into the skillet. Cook, until the sauce thickens and the chicken is warmed through. When the chicken reaches an internal temperature of 165F, it is fully cooked.
You can use chicken thighs in place of the breasts. Thighs take longer to cook, so adjust cooking time accordingly.
Double the chicken for a larger meal! You may need to sear in batches. You can use half and half in place of the heavy cream.