Line a baking sheet with parchment paper and lightly grease it with cooking spray. Set aside.

In a heavy-bottomed saucepan, combine the sugar and water over medium heat. Stir gently until sugar dissolves, then stop stirring completely. Let the mixture cook undisturbed for 6-8 minutes, swirling the pan occasionally, until it turns a deep amber color.

Remove from heat and immediately stir in the toasted hazelnuts and 1/4 teaspoon sea salt. Quickly pour the mixture onto the prepared baking sheet and spread it thin with a greased spatula. Let cool completely for 20-25 minutes until hardened.

Once cooled, break the praline into small shards and rough pieces using a knife or your hands. Set aside.

Melt the milk chocolate and coconut oil together in a microwave-safe bowl in 30-second intervals, stirring between each, until completely smooth. Alternatively, use a double boiler.

Pour the melted chocolate onto a parchment-lined baking sheet and spread it into a rectangle about 1/4-inch thick using an offset spatula.

Immediately sprinkle the praline shards evenly over the chocolate, pressing them gently into the surface so they adhere. Finish with a light sprinkle of flaky sea salt.

Refrigerate for 25-30 minutes until the chocolate is completely set and firm to the touch.

Break the bark into irregular pieces using your hands or a sharp knife. Store in an airtight container with parchment paper between layers.