How to Make It
In a large skillet, heat the olive oil over medium-high heat. Season the chicken with salt and black pepper. Add the chicken to the skillet, making sure to not overcrowd the pan. Cook until richly golden brown and seared, about 4 minutes per side. Pour in the red wine and deglaze the pan. Transfer the chicken and wine to the slow cooker.
Add the pepperoni slices, onions, diced tomatoes, chicken stock, rosemary, bay leaf, and salt to the slow cooker and cover and cook on high for 2 hours or on low for 4 hours.
The pepperoni will render some fat, skim the fat off the surface of the sauce. Remove the chicken from the sauce and transfer to a cutting board. Discard the bones and cover with foil to keep warm.
To fry the herbs leaves; bring a small saucepan with a few tablespoons of olive oil over moderately high heat. Fry the leaves very briefly for about 5 to 15 seconds until crisp. Using a slotted-spoon, transfer the sage and parsley to a paper towel to drain.
To serve, remove the bay leaf and rosemary sprigs from the sauce. Arrange the chicken in a deep-dish serving platter and pour the sauce over the top. Scatter the pepperoni slices around and over the chicken and garnish with the crispy herbs. Serve with potatoes or toasted bread.