Crock Pot Guinness French Onion Soup & Irish Cheddar Crouton — The Skinny Fork Here's the deal...I made this and it was delicious. It was a HUGE hit with my peeps. However, I had to cook it ALL NIGHT on low to get the onions to soften up and to let the spices settle in. I suggest using thyme instead of rosemary. Hubby said it's the best french onion soup he's ever had!