Line two baking sheets with parchment paper. In a large, microwave-safe bowl, combine the 4 tablespoons of butter and mini marshmallows. Microwave on high for 1 minute, stir, then microwave for another 30-60 seconds or until melted and smooth. Stir well.

Add the crispy rice cereal to the marshmallow mixture. Stir gently with a rubber spatula until the cereal is evenly coated.

Using lightly buttered hands or a piece of buttered parchment paper, press the mixture into 24-28 round, flat cookies, about 2-inches in diameter and 1/2-inch thick. Arrange them on the prepared baking sheets. Set aside while you make the caramel.

In a heavy-bottomed saucepan over medium heat, melt the 1/2 cup butter. Add the brown sugar, heavy cream, and salt. Bring to a gentle boil, stirring constantly. Reduce heat to low and simmer for 5-7 minutes, stirring occasionally, until slightly thickened. The caramel should be able to coat the back of a spoon.

Remove the caramel from the heat and stir in the vanilla extract.

Carefully spoon about 1-2 teaspoons of warm caramel over the top of each crispy cereal cookie, spreading it gently to cover most of the surface. Place the baking sheets in the refrigerator for 20-30 minutes, or until the caramel is firm.

In a small microwave-safe bowl, combine the milk chocolate chips and coconut oil (if using). Microwave in 30-second intervals, stirring between each, until the chocolate is completely melted and smooth. Be careful not to overheat.

Remove the cookies from the refrigerator. Dip the caramel-topped side of each cookie into the melted chocolate, or spoon chocolate over the caramel, allowing any excess to drip off. Place the chocolate-coated cookies back on the parchment-lined baking sheets.

Refrigerate the cookies for another 20-30 minutes, or until the chocolate coating is set. Once set, they are ready to serve and enjoy!