For the mashed potatoes: Peel potatoes and cube into uniform pieces, 8 per potato. Smash two cloves of garlic. Place potatoes and smashed garlic in saucepot, cover with water, cover pot and bring to boil. Season with salt and cook to tender, removing lid once potatoes boil. Return the potatoes and garlic to hot pot after draining, then add milk or stock and cheese and mash. Season with pepper of choice, then keep covered.
For the Dijon-tarragon chicken: While potatoes are coming to a boil, remove tenders from chicken and pound the breasts (if they are large) 1/2 inch thick, then cut each into 3 pieces. Season chicken breasts and tenders with salt and pepper.
Heat a large cast-iron skillet over medium-high heat with EVOO and melt butter into oil. When it foams, add chicken and brown on both sides, 6 to 7 minutes.
Peel and chop shallot and chop or grate garlic.
Remove chicken to a plate, add shallots and garlic and stir a minute or so. Add wine and reduce to 1/4 cup, then add stock and bring to boil. Add creme fraiche or heavy cream and simmer at low rolling boil 2 to 3 minutes, then add Dijon and juice of 1/2 lemon. Chop and add tarragon, slide chicken back into pan and leave on warm or cover pan.
For the chard with bacon and leeks: While chicken is working, heat a large nonstick skillet over medium-high heat with 1 tablespoon of olive oil, 1 turn of the pan. Stem chard and chop stems; shred the greens. Chop and add bacon to the pan and brown to crisp, 4 minutes. Quarter leek and trim root, then chop; add chard stems and leek to bacon, stir 2 minutes, then wilt in chard greens. Season with salt and pepper and nutmeg to taste, then add juice of 1/2 lemon.
Serve chicken alongside mashed potatoes and greens with bacon.