In a large pan, pour in the stock and 3 cups of cold water. Cook over medium heat and bring it to a simmer.
In a heavy bottom pan, heat butter and half of the oil and add in the chopped onions and crushed garlic. Cook till soft. Add barley and mix well. At this point, add a cup of stock mixture to the pan. Keep stirring till the water is absorbed.
Repeat the same process for the rest of the stock till the barley is tender.
Add spinach at the very end and season the mixture if needed.