Melt butter and olive oil in large dutch oven. Once butter has melted, place garlic cloves and sage leaves in pot and cook for 4-5 minutes.
Add chicken to pot and brown on each side for 5-6 minutes. Remove chicken from pot.
Add white wine and brandy to pot and deglaze, stirring constantly. Let alcohol evaporate away, then add mustard and mix together.
Place chicken back into pot and pour in chicken stock. Bring to a boil, cover, and cook for 20 minutes over medium heat.
Meanwhile, prepare cream. Whisk together cream and flour. When chicken is done cooking, remove chicken from pot. Use the back of a spoon to mash the garlic pieces.
Turn heat up to high and reduce the sauce for about 10 minutes, until it starts to thicken. Using a ladle, pour 2-3 tablespoons of sauce, a little at a time, into your bowl with cream and whisk immediately to temper the cream. Transfer cream to pot with remaining sauce and continue to whisk until sauce reaches a thick, creamy consistency.
Pour sauce over chicken pieces to serve.
For the potatoes:
Brush potatoes and onions with oil and salt. Cook them directly on a grill over medium heat until cooked through. Remove from grill and transfer to large bowl.
Mix together dijon mustard, lemon juice, and pepper flakes.
Pour dressing into potato mixture and toss.
Add peas and salt and pepper to taste.
Recipe by Things I Made Today at https://www.thingsimadetoday.com/2013/08/05/dijon-dinner-chicken-with-potato-onion-and-pea-salad/