How to Make It
Cut each mushroom stem into 8 equal slices (about 1/2-inch each); set aside. Roughly chop mushroom tops; set aside.
Heat 1 tablespoon of the oil in a small saucepan over medium-high. Add flour; whisk until combined. Whisk in cashew milk until smooth and thickened. Remove from heat, and add chopped mushroom tops, garlic, shallot, tarragon sprig, and 1/8 teaspoon of the salt. Cover; let stand at room temperature for 10 minutes. Pour through a fine-mesh strainer; discard solids. Return sauce to saucepan, and cover to keep warm.
Heat remaining 1 tablespoon oil in a medium nonstick skillet over medium-high. Add half of the mushroom “scallops”; cook until tender and browned on both sides, about 2 minutes per side. Repeat with remaining mushrooms. Sprinkle with black pepper and remaining 1/4 teaspoon salt. Spread sauce on a platter, and top with mushroom scallops; garnish with tarragon leaves.