Nonstick cooking spray
4 tablespoons unsalted butter
1 bag (10 ounces) marshmallows
1/2 teaspoon salt
6 cups toasted oat cereal
1 cup dried cranberries, or raisins
Spray a 10-by-15-inch rimmed baking sheet with cooking spray. Line with waxed paper; spray paper with cooking spray, and set aside.
In a large saucepan, melt butter over medium heat. Add marshmallows and salt; cook, stirring occasionally, until marshmallows have melted, about 5 minutes. Remove from heat, and stir in cereal and dried cranberries.
Immediately transfer mixture to prepared baking sheet. Using a spatula (or your fingers) coated with cooking spray, press in quickly and firmly. Let cool, about 1 hour; cut into 24 bars (3 rows lengthwise by 8 rows crosswise).
Store in an airtight container up to 2 days.