Preheat the oven to 450 degrees F. Line a baking sheet with aluminum foil.
Clean the radishes, removing the greens, and slice in half. Place in a medium sized bowl and toss with the olive oil. Spread cut side down in a single layer on the prepared sheet and sprinkle with the kosher salt. Roast under tender with just a bit of bite, 15-20 minutes.
Place the roasted radishes on a serving plate and drizzle with brown butter. Top with parley and black pepper. Season with additional salt if desired.
Notes
Here's a basic tutorial on how to brown butter. This recipe only calls for 1 tablespoon but brown butter is delicious and will keep in the refrigerator for just as long as regular butter. I recommend browning an entire stick of unsalted butter (4 ounces) and using the rest in place of regular butter until it runs out. It's great with pasta, eggs, vegetables, toast, etc.