Texas Crabgrass

1/2 cup (1 stick) butter, melted
1/2 cup chopped onion
1 (10 ounce) package frozen chopped spinach
1/2 pound fresh crabmeat or 1 (7 ounce) can crabmeat, drained
3/4 cup grated Parmesan cheese

In a small skillet, melt the butter and saut