Start the potatoes. Bring a large pot to a boil and add potatoes, Cook until potatoes are tender but not mushy, about 15-20 minutes. Drain and put potatoes through a ricer or use an electric mixer to mash. Add butter, half and half and mix until combined, but do not over-mash! They will turn into glue. Season to taste with salt and pepper.
Start filling. Heat oil and butter in a large saucepan over medium. Add carrots, onion, and mushrooms; season with salt and pepper, and cook until carrots are tender, 8-10 minutes. Add wine (optional) and cook another 5 minutes. Add flour, and cook, stirring until vegetables are coated for 1 minute. Gradually add milk and half & half, stirring until smooth. Cook, stirring occasionally, until mixture comes to a simmer and thickens, about 10 minutes. Stir in turkey, thyme, peas and lemon juice. Bring to a simmer and season to taste with salt and pepper. Pour filling evenly into four mini coquette dishes or casserole dish.
Put mashed potatoes into a piping bag or large plastic bag with a small part of the corner cut out. Pipe mashed potatoes onto the top of the filling, making small peaks as you go. Place in the oven and bake until golden and bubbling, 15-20 minutes. Let pot pie cool a few minutes before serving.