1. Rinse and brush the salsify first because the roots can be very sandy and dirty. Then peel them.
2. Rinse them well under cold running tap water again until all the sand and dirt is gone. While peeling the salsify, let the peeled roots soak in some water with half of the lemon juice. This keeps them from oxidation that makes the white salsify yellow once peeled.
3. Then chop the peeled salsify roots into small bits. Also peel the potato and chop it up. Peel the garlic cloves and slice them in half.
4. Place a large pan of salted water over high heat until boiling. Then add the chopped vegetables and garlic. Turn the heat a little lower.
5. Cover the pan and cook the potatoes and salsify for 12 to 15 minutes until the vegetables are tender. Then drain them all well. Return the cooked vegetables to the pan and add the unsalted butter. Season with a good pinch of pepper, salt and nutmeg to taste. Mash the vegetables well. Make the salsify puree mashed potatoes as chunky or as velvety as you like.
6. Check the seasoning of the mash and add extra pepper, salt or nutmeg to taste.
7. Then transfer the salsify puree mashed potatoes to a serving bowl and top with a little extra knob of unsalted butter. Garnish the potato mash with a last sprinkle of freshly ground black pepper. Serve hot.