Place your cereal in a bag and crush with a rolling pin. Make sure to leave a few large pieces, since the texture of the crunch is really satisfying. Set cereal aside.
In a medium saucepan over medium heat, warm the nut butter and maple syrup, stirring well to mix. Fold in the flaky salt.
Remove mixture from the heat, and stir in the crushed cereal. Thoroughly mix until combined, then spread mixture out onto a parchment-lined 7″x11″ (20x30cm) baking pan, making sure to press very firmly - especially in the corners - so that the mixture holds together. Place in the fridge or freezer to cool.
In a double boiler over a low simmer (a heat-proof glass bowl over a pot of water works great), add chopped chocolate. Melt over medium heat, stirring often.
When the bars are completely set, remove them from the freezer, let warm up for 5 minutes, then cut into 18 even pieces.
Dip each piece in melted chocolate, then place on a rack or piece of parchment to cool and set. Drizzle remaining chocolate over the top to garnish, then sprinkle with a little more flaky salt. Once cool, enjoy! Store bars in the fridge for up to one month, or the freezer for 6 months.