Blueberry Dump Cake

1 (21 ounce) can blueberry pie filling
1 (18.25 ounce) box yellow cake mix
1/2 cup butter
1/2 cup chopped walnuts

Place pie filling in crock pot. Combine dry cake mix and butter, then sprinkle over filling. Sprinkle the walnuts on top of cake mixture. Cover and cook on LOW for 2 to 3 hours.

Serve warm in bowls topped with whipped cream or vanilla ice cream.