Spray an 8x8 pan with nonstick cooking spray and set aside. Also, spray a medium pot and a rubber scraper with nonstick cooking spray.
In a medium pot, melt butter over medium-low heat. Continue to cook butter, swirling occasionally until golden brown, 7 minutes or so. Stir in marshmallows and stir until completely melted. Stir in lemon extract then remove from heat.
Pour in cereal and stir to coat in melted marshmallows. Once coated, pour the mixture into the prepared 8x8 pan.
Using lightly greased fingers, press bars down to flatten the top. Cool 15-30 minutes before cutting into squares. Top with any desired topping: lemon zest, lemon icing, white chocolate drizzle, etc.
Store in an airtight container for up to 3 days to maintain freshness.
Notes
9x18 Pan: Simply double the recipe to fit into a 9x18 glass baking dish.
Toppings: Feel free to top these lemon rice Krispie treats with lemon zest, lemon icing, or a white chocolate drizzle!
Marshmallow Bits: If you like having some unmelted marshmallow bits left in your rice Krispie mixture simply reserve 1/2 cup of marshmallows when initially adding them to the recipe. After taking the mixture off heat add cereal and reserved marshmallows and mix briefly. They will melt slightly from the heat, but not completely which is what you want.