Mash sweet potatoes with butter and cream; season with salt and pepper.
Heat two tablespoons oil in a skillet; saute greens until wilted; season with salt and pepper.
Put cornmeal in a shallow bowl; dredge shrimp in this until coated. Heat remaining two tablespoons of oil in skillet; saute shrimp until just cooked. Season with salt and pepper.
Arrange on plates in a stacked formation: sweet potatoes, greens, then shrimp. Top with corn and a sprig of thyme.