In a large saucepan over medium heat, melt the unsalted butter. Stir occasionally to prevent burning.
Once the butter is melted, add 9 ounces of the miniature marshmallows (reserve 1 ounce for later) to the saucepan. Stir until the marshmallows are completely melted and smooth.
Remove the saucepan from heat and stir in the vanilla extract and salt. Mix well.
Add the Lucky Charms cereal to the melted marshmallow mixture. Stir gently until all the cereal is well-coated.
If you’re using the optional Lucky Charms Marshmallows, fold them in at this stage for an extra treat in every bite.
Pour the mixture into a greased or parchment-lined 9x13-inch baking dish. Use a spatula to press the mixture down evenly. Be careful not to press too hard, or the bars may become too dense.
Allow the bars to cool at room temperature for about 30 minutes. For quicker setting, you can place them in the refrigerator.
Once set, cut the bars into squares or rectangles. Serve and enjoy the sweetness of your homemade Lucky Charms Bars!
