Cut the chicken in half lengthwise so that you have 8 smaller, thinner cutlets.
Salt and pepper both sides of the chicken cutlets.
Heat oil and butter in a large skillet over medium-high heat. Cook cutlets on both sides until golden brown and cooked through. Remove the cooked chicken and set aside.
Reduce heat to medium. Add the garlic and saute for 1 minute, stirring to make sure it doesn’t burn.
Add the brandy (or wine if using), being careful if cooking over an open flame. Simmer until it is reduced by half.
Add the mustards and stir to combine.
Add the cream and chicken stock, adding more stock if the sauce seems too thick.
Taste and adjust seasoning as desired.
Return the chicken to the pan, nestling into the sauce. Cook for another few minutes to ensure the chicken is warmed through and coated.