Thaw onions per package directions. Melt butter in a large skillet over medium heat. Add onions. Cook uncovered for 5-8 minutes or just until beginning to brown.
To the onions, add a splash of sherry or white wine to deglaze the pan, scrape any brown bits on the bottom. Add flour, stir gently to coat. Add chicken stock, salt, granulated garlic, white pepper, nutmeg and bay leaves.
Simmer for 3 minutes then add cream, Cook over medium heat uncovered for 5-10 minutes or just until reduced. Remove bay leaves, mix in fresh thyme and serve.
Notes
If the brand packaging isn't clear about how to thaw the onions you can place them into a colander and run under hot water for a few minutes. Drain them well and pat dry with a paper towel then proceed with the recipe. If they aren't completely thawed step 1 may take a little more time. Adjust the cooking time as needed, it will still work fine.