Place cereals in a large bowl.
In top of a double boiler or a metal bowl over hot water, melt baking chips with lemon zest and juice; stir until smooth.
Stir in butter until blended.
Pour over cereal; toss to coat.
Add confectioners' sugar and, if desired, coarse sugar; toss to coat.
Spread onto waxed paper to cool.
Store in an airtight container.
