In a large container, pour in 1 bottle of wine and add the capon. Refrigerate, covered, for 24 hours.
Heat 3 tablespoons butter in a large skillet over medium-high heat. Remove the capon from the marinade, and reserve the marinade. Add the capon parts to the skillet and sear on all sides, about 5 minutes per side. About halfway through the searing process add the chopped bacon.
Put the capon marinade in a large Dutch oven over medium heat. Stir in the onion, thyme, bay leaves, carrots and garlic. Add the seared capon and bacon and pour in the remaining half bottle of wine to cover the capon. Partially cover the pot with a lid and let simmer for 45 minutes.
Add the chopped mushrooms and potatoes to the Dutch oven and let simmer for another 10 minutes. Add the roux, stir to combine and let simmer for another 10 minutes. Transfer to a large serving bowl and serve.
In a small pot, melt the remaining 3 tablespoons of butter over medium heat. Add the flour and cook until thick and light brown in color. Whisk in about 1 cup of the simmering wine and stir until incorporated.
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