Preheat the oven at 450º and position the rack in the middle of the oven.
Place a hen, breast side down on a cutting board. Remove the backbone by cutting along both sides with shears or a large sharp knife.
Flip the hen and flatten it by pressing down on the breastbone with your palm. Split the hen in two along the breastbone. Repeat with the remaining hen.
Place on a heavy roasting pan and spread on each half, ¼ of a teaspoon of butter, Herbs de Provence, salt and pepper, and a drop of olive oil. Place in the hot oven and cook for 30 to 45 minutes. Poke the hen while cooking to release any juices.
When done, remove from the oven, place the hen in a dish and cover with aluminum foil and let rest.
FOR THE WHISKEY AND CREAM SAUCE
Place the unwashed cooking pan over the stove and add the remaining 2 tablespoons of butter and let it melt. Lower the heat and add the whiskey, very slowly. With a wooden spoon scrape up any bit on the pan.
Add the shallots and cook until tender, 1 minute. Add the Worcestershire sauce, mustard and raise the heat to medium-high. Bring to a boil stirring constantly
Add the heavy cream and the lemon juice. Taste the sauce and season with salt and pepper.
Serve hot over the Cornish hen.