Sprinkle raisins evenly in ungreased 10 x 6 x 2-inch (1 1/2-quart) glass baking dish. Place KELLOGG'S FROSTED MINI-WHEATS Big Bite cereal, frosted side up, in single layer over raisins. Set aside.
In medium-size mixing bowl, beat eggs until foamy. Add sugar, salt, vanilla, and butter, mixing only until combined. Scald milk. Gradually add hot milk to egg mixture, stirring constantly until margarine is melted. Pour milk mixture evenly over biscuits.
Bake at 300°F about 1 hour or until knife inserted near center comes out clean. Cut into squares. Serve warm with half-and-half or ice cream.