Peel the carrots, quarter them lengthways and cut across into fork-sized pieces. Melt the butter in the saucepan and stir in the sugar until it has melted. Add the carrots and toss briefly. Pour in the vegetable stock and sauté the carrots for about 10 minutes until they are firm to taste.
Mix the mustard with the carrots and season with salt, pepper and lemon juice. If you like it a little thicker, you can add some crème fraîche or cream cheese.