01 - Line an 8x8-inch baking dish with parchment paper, leaving overhang on the sides for easy removal.
02 - In a saucepan over medium-low heat, combine the peanut butter and maple syrup. Stir continuously until smooth and warmed through, about 2 to 3 minutes. Remove from heat and stir in the vanilla extract and sea salt.
03 - Gently fold the crushed cornflakes into the peanut butter mixture until evenly coated, taking care not to over-crush the cereal.
04 - Transfer the mixture to the prepared baking dish and spread it evenly, pressing it firmly and flat with a spatula. Place the dish in the freezer for 20 to 30 minutes until the layer is firm and set.
05 - Remove the set slab from the dish using the parchment overhang and cut into 16 even bars using a sharp knife.
06 - Combine the dark chocolate chips and coconut oil in a microwave-safe bowl or double boiler. Heat in 30-second intervals, stirring between each, until completely smooth and glossy.
07 - Dip each bar into the melted chocolate, coating all sides thoroughly. Allow excess chocolate to drip off, then place each coated bar onto a parchment-lined tray.
08 - Place the tray in the refrigerator for 15 to 20 minutes, or until the chocolate coating is fully set and firm to the touch.
09 - Transfer the finished bars to an airtight container and store in the refrigerator. Bars can also be frozen for up to 3 months.