Soak sliced potatoes in salted water for about 20 minutes. Meanwhile, bring medium pot of water to boil. Drain potato slices and plunge them into boiling water for 1 minute. Rinse slices in cold water and lightly dry. Place potato slices in bowl and lightly coat with olive oil. Set aside.
Preheat oven to 400°F. To make béchamel sauce, warm milk and cream over low heat in small pan. In another pan, melt butter over medium-low heat and add flour and cook 1 minute, stirring. Add milk and cream gradually, about 1/4 at a time, stirring between each addition until smooth. Mixture should be velvety and slightly thick. Add salt, pepper and nutmeg to taste.
Place cooked penne pasta in mixing bowl and add 3/4 of béchamel sauce; stir to coat.
Fill each cocotte or ramekin with 3/4 cup of béchamel coated pasta, and press down with back of spoon. Top with heaping spoonful of the remaining béchamel.
Arrange the potato slices on the top of each cocotte, overlapping each slightly.
Bake 10 minutes or until potatoes lightly brown on edges. Place 1 slice of raclette on top of each cocotte and return to oven for another 10 minutes or until raclette is melty and lightly browned.
Serve each cocotte, hot, with cornichon relish on side.