How to Make the Ultimate Umami-Bomb Vegetarian Demi-Glace
2 pounds Yukon Gold potatoes, peeled and cut into 2-inch chunks
4 tablespoons unsalted butter
1/2 cup whole milk
Freshly ground pepper
In a large saucepan, cover the potatoes with cool water, season generously with salt and bring to a boil over high heat. Reduce the heat to moderately high and boil the potatoes until tender, about 20 minutes. Drain well, then return the potatoes to the saucepan.
Meanwhile, in a small, sturdy glass bowl, melt the butter in the milk in a micro-wave oven, about 1 minute. Pour the milk mixture over the potatoes. Using a potato masher, mash the potatoes until smooth. Season with salt and pepper and serve.