Step 1
Combine 1½ lb. parsnips, peeled, trimmed, quartered lengthwise, cut into eighths if large, 2 Tbsp. unsalted butter, cut into pieces, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, ½ tsp. ground coriander, and 1 cup water in a cold large skillet. Set over medium heat, cover, and cook until parsnips are fork-tender, 12–15 minutes. Uncover and continue to cook, tossing parsnips occasionally, until liquid is evaporated and parsnips are deep golden brown around edges, 8–10 minutes.
Step 2
Meanwhile, combine ¾ cup salted, roasted peanuts, preferably cocktail, coarsely chopped, 1 tsp. crushed red pepper flakes, 1 tsp. ground cumin, and remaining 1½ tsp. ground coriander in a small nonstick skillet over medium heat; if using dry-roasted peanuts, add 2 tsp. vegetable oil to pan. Cook, tossing often, until fragrant, about 1 minute. Remove from heat and stir in 2 tsp. sugar and remaining ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt.
Step 3
Stir juice of ½ large lemon, 1 garlic clove, finely grated, ½ cup plain whole-milk Greek yogurt, and 2 Tbsp. extra-virgin olive oil in a small bowl to combine; season with salt.
Step 4
Spread yogurt sauce on a platter. Arrange half of parsnips on top and sprinkle with half of spiced peanuts. Top with remaining parsnips, then spiced peanuts. Scatter some coarsely chopped parsley over.