Add the halved radishes to a baking sheet and toss with 1 teaspoon of olive oil. Season with a pinch or two of salt and pepper. Roast for 15 minutes. Add the green beans to the same sheet pan. Drizzle with the remaining 1 teaspoon of olive oil and season with a pinch of salt and pepper. Roast for an additional 10 minutes.
While the vegetables are roasting, prepare the blue cheese butter. Add the softened butter and blue cheese to a mixing bowl. Beat together until smooth, adding in the half-and-half to create a smooth, dip-like consistency.
Spoon the butter into a small ramekin or bowl. Transfer the radishes and beans to a platter. Squeeze the juice of ½ lemon over the vegetables and sprinkle with flaked sea salt or fleur de sel. Serve with the butter.