Slice the onions into 0.5 cm thick pieces.
No need to peel the apples. Quarter each apple, remove the core from each quarter. Then slice each quarter into 4 wedges.
Thinly slice the garlic cloves.
Bring the duck breasts to room temperature, pat them dry with a paper towel.
Using a sharp knife, make long diagonal cuts along the skin of the duck breasts every 0.5 cm. The cuts should cut all the way through the duck skin but not cut the meat. Once done, make another set of cuts at 90 degrees to create a diamond pattern. Making these cuts will help the duck fat render.
Generously season the duck breasts with salt and pepper. I only use a little bit usually as I don't salt my food much.
Heat one tablespoon of olive oil in a heavy bottom pan on medium-high heat.
Add the duck breasts to the pan skin side down and cook without moving for about 6-8 minutes. Once the skin is properly seared and crispy, the duck breasts will very easily release from the pan. If you try to lift the duck breasts and they are really sticking to the pan then let them cook for another minute or so.
Once seared, remove the duck breasts to a plate skin side up.
Drain all the fat from the pan into a bowl to use for the next step.
Return the pan back to the stove, add a little bit of the saved duck fat (about 1/2 a tablespoon) and add the sliced onions. Cook on medium heat stirring occasionally for 10 minutes until the onions just begin to soften and slightly turn colour. You may need to add a bit more duck fat as needed.
Add the sliced garlic and cook for another 1-2 minutes.
Add the vermouth to deglaze the pan and scrape to get all the onion and duck bits from the bottom. Let the vermouth evaporate.
If desired, add a bit more duck fat (1-2 teaspoons) to the pan, add the apple wedges, thyme leaves, and mix well. Season with salt and pepper to taste.
Move the apple-onion mixture around to create space for the duck breasts. Return the duck breasts to the pan and nestle them between the apple-onion mixture skin side up.
Add the stock to the pan, bring it to boil. Reduce the heat to low so that the mixture just simmers, cover the pan tightly with a lid and cook on low for 1.5 hours.
After 1.5 hours, remove the lid, turn the heat up to high and cook for about 3-5 minutes to reduce the sauce a bit.
Once the sauce is reduced, add half a cup of frozen cranberries, mix them in with a spoon and transfer the pan to the oven turned to broil.
Broil for about 3-5 minutes or until the skin gets crispy again. Make sure to watch the oven carefully as broiling can turn the food from beautifully golden and crispy to dark and burnt in about 45 seconds if you leave it too long.
Serve with mashed potatoes, steamed vegetables, quinoa, rice, or, for a more authentic Russian meal, with buckwheat.