Melt 1/4 cup of butter in a large skillet over medium heat. Add mushrooms and onions. Season with 1/4 teaspoon salt and 1/4 teaspoon pepper.
Cook, stirring often until vegetables are softened. Remove to a bowl and set aside.
Add remaining 1/4 cup of butter to the skillet with flour. Cook over medium heat, whisking until browned to a light peanut butter color.
Add whiskey and broth, whisking until combined, cook about 2 minutes.
Stir in mushrooms and onions.
Whisk in cream.
Season with brown sugar, remaining salt and pepper. Cook until thickened.
Keep warm until ready to serve.
!For the Ribeyes
Bring steaks to room temperature.
Brush or spray with olive oil and season with salt and pepper
Prepare a grill fire to 350° with hickory.
Cook steaks over indirect fire with the grill closed about 7 minutes.
Flip steaks and continue to cook until internal temperature reaches 130° for rare or until desired doneness.
Remove steaks from the grill and allow to rest 10 minutes before serving with mushroom cream sauce.