Remove greens from radishes, wash, roughly chop and set aside.
Wash and dry radishes, then trim off the root and stem. Cut medium radishes in half and large ones into quarters, creating approximately even-sized pieces.
Mix butter and miso in a small bowl until well combined.
Heat oil over medium-high heat in a large skillet until shimmering.
Add radishes in a single layer, cut side down, and sear without disturbing for 4-5 minutes, or until golden brown.
Toss, add pepper and sauté 3-5 minutes longer, stirring occasionally, until radishes are tender. You may add a splash of water and cover for a couple of minutes if necessary. They should be easily pierced with a fork.
Lower heat, add radish tops and stir 1-2 minutes, or until greens are wilted.
Remove from heat and stir in the miso butter until melted and evenly coated.
Add a generous squeeze of lemon, season to taste with additional salt if needed, and serve immediately.