Double the Spoonfuls

0 Line a 9x13-inch pan with parchment paper and lightly spray with cooking spray.
1 In a large pot, melt the butter over medium heat, then add the mini marshmallows. Stir and continue stirring until the marshmallows are completely melted. They won't seem like they're incorporating with the butter at first but they eventually will. Add the vanilla extract and salt and stir to combine.
2 Remove from the heat and add the cereal. Use a wooden spoon to stir until the marshmallow is evenly distributed and all of the pieces of cereal are coated. Make sure to get any remaining marshmallow from the bottom of the pot. If your pot is too small, you can also transfer the mixture to a very large bowl to combine everything more easily.
3 Pour the mixture into the prepared pan, and use a greased rubber spatula to gently spread it evenly, making sure not to press them down too hard or the treats will be dense.
4 Let sit at room temperature for roughly 1 hour (see note), then remove from the pan and cut into 16 rectangles by cutting the whole thing in half lengthwise then cutting 2 rows of 8 rectangles.
7 Set a large wire rack on parchment paper and lightly spray it with baking spray.
6 Melt milk chocolate melting wafers in a small bowl. Once completely melted, dip the top and sides of each rectangle about halfway up, then let any excess melted chocolate drip off. You can dip the bottoms if you want to, but I personally find it just makes them a little messier and can make them stick to the wire rack. Set each on the wire rack until chocolate has fully hardened (see note).
8 Melt the dark chocolate in a small bowl then pour into a ziplock bag. Cut just the tip off one corner, then drizzle each milk chocolate section of the rice krispies treats with the dark chocolate. Sprinkle with flaky salt right away, let the chocolate set, then enjoy immediately for the best texture!