In a small bowl, beat butter and sugar until crumbly, about 2 minutes. Add egg; mix well. Beat in eggnog and vanilla. Combine the flour, baking powder, nutmeg and salt; add to creamed mixture just until moistened. Fold in pineapple.
Fill greased or paper-lined muffin cups three-fourths full. Combine topping ingredients; sprinkle over muffins.
Bake at 400° for 18-22 minutes or until a toothpick inserted in muffin comes out clean. Cool for 5 minutes before removing from pan to a wire rack. Serve warm. Yield: 9 muffins.