Preheat the oven to 400°F (200°C). Scrub potatoes and dry with a clean towel. Oil potato skins with olive oil and sprinkle with sea salt.

Bake potatoes directly on a rack in the center of the preheated oven until tender when pierced with a fork, about 55 minutes.

In a large skillet over medium heat, melt butter. Add onions and cook for about 2 minutes, then add mushrooms, salt, and pepper. Cook until mushrooms are golden, stirring often, about 5 to 8 minutes.

Stir in garlic and cook until fragrant, about 30 seconds.

Add white wine, scrape up any browned bits on the bottom of the skillet, and cook, stirring, for 1 to 2 minutes.

Sprinkle flour over the skillet, stir to moisten all the flour, and allow to cook for about 1 minute.

Combine broth and Dijon mustard. Pour the mixture into the skillet, stirring quickly to ensure no lumps of flour. Bring to a boil and cook for 3 to 4 minutes.

Add cooked chicken to the skillet and stir. Once the mixture begins to bubble and the chicken is warmed through, remove from heat and stir in sour cream.