Heat butter in a 12-inch skillet over medium-high heat until foam subsides.
Add scallions to butter. Cook, stirring occasionally, until softened (about 5 minutes). Add corn kernels and 1/2 teaspoon each of salt and pepper and cook, stirring occasionally for another 5 minutes.
Stir together cream and cornstarch in a small bowl until thoroughly combined, then add to corn and simmer, stirring, until slightly thickened, about 3 minutes.
Transfer 1 1/2 cups corn mixture to a blender with garlic and purée until smooth. Return to skillet and cook, stirring constantly, until just heated through.