To make the sauce: In a medium saucepan over medium-high heat, melt the butter. Add the onion and cook until tender, about 3 minutes, stirring occasionally to prevent browning. Add the garlic and cook for 1 minute more, stirring occasionally. Remove the saucepan from the heat, carefully add the bourbon, and return the saucepan to the heat [watch out; it might flame]. Once the flame subsides, reduce the heat to medium and add the beef stock and cream. Simmer until about 1/3 cup liquid remains, 15 to 20 minutes, stirring occasionally [times will vary depending on the diameter of your pan]. Add the thyme. Season with salt and pepper to taste.