Preheat the oven to 400 degrees. While oven is preheating, place a cast iron skillet inside to heat for 20-30 minutes.
Use a mallet to beat the chicken breasts into thin (¼") slices. Set aside. Heat 1 tbsp. of the bacon fat in a large skillet. Add the shallots and garlic and saute for 1 minute. Add 1 package of mushrooms and cook for 2-3 minutes, until they start to soften. Add 1 tbsp. of the sherry and cook down for about 5 minutes, until moist of the moisture has evaporated and mushrooms are soft.
Combine the cooked mushrooms with the ricotta cheese in a bowl and mix to combine. Lay 1 chicken breast out and spread on ricotta mixture, about ¼" thick. Roll the chicken breast up and secure all sides with toothpicks. Do the same for the remaining 3 breasts and season with 1 tsp. salt and ¼ tsp. pepper; set aside.
Add the remaining bacon fat to the skillet and add the second package of mushrooms and the crumbled bacon. Cook until mushrooms start to soften and add the remaining 1 tbsp. of sherry. Cook about 5 minutes, or until most liquid has evaporated and mushrooms are soft.
Add the ¼ tsp. salt, ⅛ tsp. pepper and heavy cream to the skillet and bring to a simmer. Simmer about 5 minutes, until cream has started to reduce and thicken. Remove from heat and set aside.
Remove the cast iron skillet from the oven after heated and add 1 tsp. of the bacon fat to the skillet. Add the chicken and brown on all sides, about 3 minutes per side. Cover in the reduced mushroom cream sauce and place in the oven for 10-15 minutes, or until chicken is fully cooked to an internal temperature of 165 degrees.
Notes
If you can't find thin sliced chicken breasts at the store, use regular chicken breasts and slice them in half lengthwise.
If you don't have sherry, you can substitute any red or white wine, or beef broth. However, for the best flavor I highly recommend using sherry.
Any kind of mushrooms can be used. Experiment with white, baby bells, portabello, cremini, shiitake, etc.
To make the chicken ahead of time, Follow all the steps to stuff your chicken. Place the stuffed breasts in an airtight container and store in the fridge overnight. Make the mushroom cream sauce and store in a separate airtight container. When you're ready to cook, heat the cast iron skillet in the oven for 20 minutes, then follow the rest of the recipe instructions for cooking the chicken. **Note you can also brown the chicken in advance and store in the fridge overnight.
To freeze leftovers: Place any leftovers in an airtight container and freeze for up to one month. Thaw in the fridge overnight and reheat in the microwave or in the oven for 10-15 minutes, until warmed through.