- 1 shallot, finely chopped
- 2 sprigs tarragon, plus 2 teaspoons chopped
- 1/2 teaspoon black peppercorns, crushed
- 1 tablespoon white wine vinegar
- 1 cup plain whole-fat Greek yogurt
- 2 tablespoons fresh lemon juice
- 1 tablespoon olive oil
- Kosher salt
- 1 tablespoon coriander seeds
- 1 teaspoon kosher salt
- 1 teaspoon mustard powder
- 1 teaspoon paprika
- 12 ounces maitake or oyster mushrooms, torn into large pieces
- 2 tablespoons olive oil
- Torn tarragon sprigs (for serving)
- A spice mill or a mortar and pestle
- Bring shallot, tarragon sprigs, peppercorns, vinegar, and 1/3 cup water to a boil in a small skillet over medium heat and cook until liquid is nearly evaporated, 8–10 minutes. Let cool. Discard tarragon sprigs and transfer mixture to a small bowl. Add yogurt, lemon juice, oil, and chopped tarragon and mix well; season with salt.
- Prepare a grill for medium heat. Finely grind coriander seeds in spice grinder or with mortar and pestle. Transfer to a small bowl and mix in salt, mustard powder, and paprika.
- Drizzle mushrooms with oil in a medium bowl; gently toss to coat. Season with rub. Grill, turning occasionally, until browned and tender, 6–8 minutes. Serve over yogurt topped with tarragon.
- Yogurt can be made 3 days ahead. Cover and chill.