Take thawed turkey out of the fridge while you prep the veggies. I like to keep it in the bag still, but in my kitchen sink.
Preheat the oven to 350 degrees F.
Gather a large roasting pan, and place the turkey size oven bag in it. Pour 1 TBSP gluten free all purpose flour blend into the bag and holding it closed, shake the bag. Place bag back into roasting pan.
Cut off outer skin of onions, and slice them into "rings". Place the onions in the bottom of the oven bag. Chop the carrots and celery and also place them in the bag. Pour in the peppercorns, and place the bay leaves.
Pour in 1 cup of organic chicken stock on top of the veggies.
Open the turkey bag and remove the gravy packet-throw that away. Then carefully remove the turkey and rinse well. Pat dry if you want, but I never do that. Repeat for the second turkey breast. Place them in the oven bag.
In a large bowl, melt the butter in the microwave. Make sure to cover your bowl in case you get splatters. Pour melted butter onto the tops of each turkey breast, trying to cover all the skin areas.
In a small bowl, mix the sea salt, black pepper, sage, thyme, and chives. Sprinkle on the tops of the turkey breasts. And gently rub in if necessary.
Close bag with the tie provided in the oven bag kit. Using a sharp knife cut 5-6 slits in the top of the bag.
Turn oven down to 325 degrees F. Place roasting pan in your oven on the LOWEST rack. You will need to remove all other racks as the bag expands while cooking. Cook for 2 hours and 30 minutes. I like my turkey cooked to at least 180 degrees F. To me, this achieves the best texture. I have even let it cook until 200 degrees and it is still perfect every time.
Remove the roasting pan from the oven. Carefully cut open a hold in the top of the oven bag and gently lift out the turkey breasts and place them in another pan or baking sheet to rest. Cover loosely with foil and let rest for at least 30 minutes before slicing.
In the meantime, gather a medium sauce pan and a metal sieve, with an oven mitt carefully lift the oven bag with drippings and veggies. Place it over the sieve. Carefully cut a few slits in the bottom of the bag to let all the dripping drain out into the sieve and then into the pan.
When all the drippings are drained, set oven bag aside and take off the sieve. On medium heat, bring the drippings to a boil. While it is coming to a boil, mix 1 C chicken stock with the 3 heaping TBSP of gluten free cornstarch. Mix will with a small whisk.
Once drippings have come to a boil, slowly add the stock/cornstarch mixture while continuously whisking. Once all that is added, taste your gravy and add more sea salt, black pepper, sage, and thyme as needed. I always need to add a little bit of each. (If you feel like your gravy still needs more thickening, mix up another 1/2 C stock and 1 1/2 heaping TBSP cornstach and slowly add that as needed).
Slice turkey breasts. Serve with mashed potatoes and this delicious homemade gravy.