For the Brussels sprouts: Bring a large pot of water to a boil. Add the Brussels sprouts and blanch until tender-crisp. Drain and rinse with cold water to stop the cooking; set aside.
Heat a saute pan to medium-high heat and add the oil followed by the onions and garlic. Sweat the onions and garlic for a few minutes. Add the Brussels sprouts and sear until golden brown, about 2 minutes. Deglaze with the chicken stock and then swirl in the butter. Reserve.
For the mashed potatoes: In a large pot filled with water, add the potatoes and bring to a boil over medium-high heat. Lower to a simmer and cook until the potatoes are fork-tender. Drain the potatoes in a colander and transfer them back to the pot. Add the cream, butter and salt and pepper to taste and mash until smooth. Reserve.
For the mushroom madeira sauce: Heat a saucepan over medium heat and add the butter. Add the onions and sweat for a few minutes. Add the mushrooms and thyme and cook over medium-high heat until slightly caramelized. Deglaze the pan with the Madeira and cook out the alcohol for about 1 minute. Add the heavy cream and reduce by a third. Lower the heat, add the demi-glace and simmer until the sauce coats the back of a spoon. Season with salt and pepper.
For the pork chops: Sprinkle the pork chops with salt and pepper. Add some oil to a hot saute pan and sear the chops for about 4 minutes. Flip and cook on the other side until the internal temperature reaches 155 degrees F, another 4 minutes. Remove the pan from the heat, drain off any excess oil and deglaze with the Madeira, leaving the pork in the pan. Return to the heat and cook off the alcohol for about 2 minutes. Reserve.
To create the plate: Place some mashed potatoes on the center of each plate. Follow with some Brussels sprouts. Place a pork chop on top and spoon sauce all over.