Step 1 Preheat the oven to 375°F and set an oven rack in the middle position.
Step 2 Place the beef, baking soda, 1 teaspoon of the salt, and 1 tablespoon of water in a medium bowl. Mash with your hand to combine. Set aside for 20 minutes.
Step 3 While the meat tenderizes, place the potatoes in a medium saucepan and add just enough cold water to cover them. Bring to a boil over high heat, then reduce the heat to medium-low and simmer, uncovered, until the potatoes are soft and fork-tender, 8 to 10 minutes. Drain the potatoes and return to the saucepan. Place the pan over medium heat and stir the potatoes with a wooden spoon or potato masher until they are dry and fluffy, about 3 minutes. Remove the pan from the heat and add the sour cream, butter, half & half, and the remaining teaspoon of salt. Using a potato masher, stir and mash the potatoes with the other ingredients until smooth. Taste and adjust seasoning, if necessary. Set the mashed potatoes aside.
Step 4 Heat a 12-inch oven-proof skillet over medium heat. Add the bacon and cook, stirring frequently, until crisp, 6 to 8 minutes. Using a slotted spoon, transfer the bacon to a paper towel-lined plate, leaving the fat in the pan. Add the onions and carrots to the bacon fat and cook, stirring frequently, until softened and starting to brown, 6 to 8 minutes. Add the garlic and cook 1 minute more. Add the wine and increase the heat to high; bring to a boil, scraping any brown bits from the bottom of the pan, until the liquid is reduced by about half. Add the flour and stir until dissolved. Add the reserved ground beef mixture, tomato paste, and Worcestershire sauce; continue cooking on high heat, breaking the meat apart with a spoon, until the meat is no longer pink, about 5 minutes. Add the chicken broth; bring to a simmer, reduce the heat to low, and cook, scraping any brown bits from the bottom of the pan, until thickened, about 2 minutes. Stir in the thyme, pepper, peas, and reserved bacon, and cook until the peas are warmed through. Taste and adjust seasoning, if necessary.
Step 5 Dollop the mashed potatoes evenly over the filling. Use a rubber or offset spatula to spread the potatoes evenly over the stew and all the way to the edges of the skillet. Drag a fork across the top to make ridges. Place the skillet on a baking sheet or large sheet of foil to catch any drips and bake until the filling is hot, the topping is lightly browned, and the edges are bubbly, about 30 minutes. (For more color, turn on the broiler and broil for the last 5 minutes, or until the top is golden.) Sprinkle with chives and serve.
