Line your square dish with parchment paper for easy removal later. Set aside.
In a large saucepan over low heat, melt the butter gently, stirring occasionally, until it’s fully melted and fragrant—about 2 minutes. You’ll notice it bubbling softly and smelling rich and buttery.
Add the mini marshmallows to the melted butter. Stir constantly as they melt into a glossy, gooey mixture, about 3-5 minutes. The marshmallows will break down completely, creating a sweet, sticky sauce that fills your kitchen with a sugary aroma.
Remove the pan from heat. Gently fold in the Rice Krispies cereal and sprinkle with sea salt, mixing until every piece is coated and the mixture is sticky but easy to work with, about 1-2 minutes. The cereal will crackle softly as it combines with the marshmallow goo.
Transfer the sticky mixture into your prepared dish. Use a spatula to press it down firmly and evenly, making sure it’s compacted so the bites hold together nicely. Let it set at room temperature for about 30 minutes, or chill in the fridge for 15 minutes for quicker firming.
Once set, lift the block out of the dish using the parchment paper and place it on a cutting board. Use a sharp knife to cut into 12 equal squares or rectangles, applying gentle pressure to keep slices clean and neat.
If you like, melt the dark chocolate chips in a microwave-safe bowl in 20-second bursts, stirring each time until smooth. Drizzle the melted chocolate over the bites or dip half of each for an extra decadent touch. Let the chocolate set for about 10 minutes before serving.
Arrange the finished bites on a platter and sprinkle a pinch of flaky sea salt on top for a salty crunch. Serve at room temperature for the best texture—crispy outside with a gooey center.
