Line an 8x8 baking pan with foil and lightly grease with cooking spray or butter.
In a large bowl, mix together Lucky Charms, quick cooking oats, white chocolate chips (if using), and sprinkles (if using).
In a small saucepan over medium-high heat, stir together butter, brown sugar, honey, vanilla extract, and salt. Let mixture come to a boil, then lower heat and let simmer for about 2 minutes.
Pour liquid mixture over dry ingredients and toss well to coat.
Pour mixture into the prepared pan and using fingers, press down into an even layer.
Place pan in refrigerator for at least one hour to allow granola bars to cool and harden. Once chilled, remove from pan, place on cutting board, and cut into 10 bars (I make 5 cuts across and then one in the middle to divide into 10).