High in zinc and iron, oysters star in this velvety stew, which is also packed with beta-carotene, courtesy of flavorful sweet potato.
Melt butter and oil in a medium saucepan on medium heat. Add ginger, leeks, and potato; cook, stirring occasionally until soft, 10 to 15 minutes. Stir in flour; cook for 1 minute.
Raise heat to medium-high and slowly pour in milk and reserved oyster liquor (1/4 cup), whisking constantly. As soon as bubbles begin to form around the edges of the pan, gently stir in oysters and cook just until set, about 2 minutes. Season to taste with salt and pepper. Divide among bowls.
If you have your fishmonger shuck oysters for you, be sure to ask for the liquor (the liquid that escapes during shucking); it adds a lot of flavor.