Grease a 9 x 9 inch square baking pan with butter or cooking spray. Set aside.
In a large saucepan, melt the butter over low heat. Add the marshmallows and stir until completely melted and well combined. Remove the saucepan from heat and stir in the vanilla extract.
Add the Rice Krispies cereal with a spatula to the marshmallow mixture and gently fold until the cereal is evenly coated.
Transfer the mixture into the prepared 9 x 9-inch pan. Use a buttered spatula or parchment paper to evenly press the mixture into the pan.
Allow the Rice Krispie mixture to cool and set in the pan for about 30 minutes.
Once the mixture is completely cooled and set, use a sharp knife to cut it into squares or rectangles.
In a microwave-safe bowl or using a double boiler, melt the chocolate until smooth, in 15 second intervals, stirring in between each. Add a teaspoon of oil to chocolate if needed to to thin it out and stir in until smooth.
Prepare parchment lined baking sheet.
Insert a popsicle stick into cooled Rice Krispie Square, if desired, otherwise you can use your hands and dip the top or side of each square into the melted chocolate.
Dip each Rice Krispie treat into the melted chocolate, coating the top 1 inch evenly. Allow any excess chocolate to drip off.
Immediately sprinkle with your favorite toppings, such as colorful sprinkles or chopped nuts, before the chocolate sets. You can also drizzle with white chocolate for contrast.
Place them on the parchment paper lined pan to set, which usually takes a few minutes at room temperature or quicker if you refrigerate or freeze them briefly.
Once the chocolate is fully set, serve and enjoy!