Add plastic wrap to a mini cocotte making sure you have extra to hang over the sides.
Using a box grater, grate radishes until you have about ½ cup. Using a clean towel, press the radish gratings to remove excess water.
Slice 4-5 remaining radishes into quarters and set aside. Add the softened butter to a bowl and add radish gratings. Mix until combined. Scoop a heaping tablespoon of the butter into the bottom of the Mini Cocotte and using a knife or spatula, smooth it out in an even layer. Add a few slices of the radishes to the center.
Repeat with another heaping tablespoon and another few slices of radishes. You should be able to do this about 3 times to get to the top of the mini cocotte. Transfer to the fridge and let harden, 4-6 hours.
When the radish butter has firmed up, slice and serve with fresh sourdough bread, lemon zest, flaky sea salt and pepper.