To make the potatoes: Boil the potatoes in salted water until tender, about 15 minutes. Drain and cut in half.
To make the buckwheat pancakes: In a big bowl, add the flour, milk, 1/2 cup water, salt and egg, and whisk to make a smooth batter. Cover and let rest for 30 minutes.
Heat a nonstick pan over medium heat and add the butter. Pour in 1/4 cup of batter per pancake. When the top of the pancake gets small bubbles and the bottom is lightly browned, gently turn it over and cook until lightly browned on the other side, about 2 more minutes.
To make the raclette sauce: Heat a small pot over medium-low heat and add the half-and-half; do not let it boil. When it begins to steam, take the pan off the heat and throw in the cheese and freshly cracked pepper. Put back on low heat and stir until melted. Cover and keep warm.
Place a few pancakes on a big plate. Add 1/2 cup of the new potatoes and ladle on 1/4 cup of the sauce. Drizzle with maple syrup and serve with gherkins on the side.