Preheat your broiler and set a rack so that the food is about 3 inches from the heat. Melt the 2 tablespoons butter in the skillet over medium heat. When it stops foaming, add the garlic and stir until fragrant, about 30 seconds. Press out excess water from the chard in the colander, then transfer to the skillet with the salt and pepper. Cook, stirring and breaking up the chard. Add the cream and Parmesan and bring to a simmer over medium-high heat. The chard will continue to release some moisture. After 4 minutes, transfer the chard to a 2-quart baking dish using tongs or a slotted spoon. Continue simmering the cream sauce until thickened, 3 to 4 minutes, then pour over the chard. Top with the walnut mixture and run under the broiler until nicely browned, about 1 minute.