Mix the fennel seeds, juniper berries, salt and pepper in a small bowl. Place ⅔ of the butter in a bowl, suspend over a gently simmering bain-marie, ensuring that the bowl does not touch the water. Melt the butter while stirring constantly, remove the bowl, stir in the rest of the butter, leave to cool for approx. 3 mins. Dip the radishes in the butter, sprinkle with the spices, transfer to a plate lined with baking paper, cover and chill until ready to serve.