Morels vary in size; look for larger ones for stuffing.
Fill a medium stockpot with water; add potatoes and 1 tablespoon salt. Cover, and bring to a boil. Reduce heat to medium high; boil gently, uncovered, until tender, about 45 minutes. Drain. Hold potatoes in a clean kitchen towel, and peel. Pass potatoes through a ricer into a medium bowl. Cover with foil, and set aside.
Meanwhile, fill a large bowl with cool water. Add 1 teaspoon salt and lemon juice. Place morels in the bowl for about 3 to 4 minutes, pushing them down into the water several times to clean them. Drain on paper towels. Gently pat dry; let stand to dry while continuing recipe.
Place ramps in cold water; let stand for 5 minutes to rid them of dirt and sand. Lift out of the water, drain in a colander, and pat dry. Melt 1 tablespoon butter in a small skillet over low heat. Add ramps, 1/4 teaspoon salt, and 1/8 teaspoon pepper; saute until soft and translucent, about 10 minutes.
In a small saucepan (or in the microwave), combine 2 tablespoons butter, cream, and milk; bring to a boil. To the riced potatoes, add ramps, butter-cream mixture, Parmesan, remaining 3/4 teaspoon salt, and remaining 1/8 teaspoon pepper; mix to combine well.
Preheat oven to 350 degrees. Fill a pastry bag with 1/4-inch round tip with mashed potatoes. Insert the tip into the opening at the top of a morel, and pipe potato mixture in until morel is full. Transfer to a baking sheet. Repeat process with remaining potatoes and morels. (Stuffed morels can be prepared up to this point 1 day in advance and stored, covered, in the refrigerator.)
In a small saucepan (or in the microwave), melt remaining 2 tablespoons butter over medium-low heat. Brush tops of morels with butter, and transfer to the oven. Bake until morels are tender and potatoes are hot and slightly golden, about 20 minutes if morels are baked right away and 30 minutes if prepared the day before. Serve immediately on a bed of reserved ramp greens.