Crispy, Crunchy Homemade Nutella (Chocolate-Hazelnut Spread)

To Make the Brittle: Lightly grease a half-sheet pan and set aside. Combine water, golden syrup or corn syrup, sugar, salt, and prepared hazelnuts in a 3-quart saucier over medium heat. Scrape and stir with a heat-resistant spatula until sugar has dissolved and the candy begins to bubble around the edges, about 5 minutes. If this takes substantially more or less time, this is simply an indication that the heat level needs adjustment due to equipment variation.

Continue cooking and stirring until the candy darkens to a tawny amber or foxy brown, registering between 320 and 340°F (160 and 171°C) on a clip-on digital thermometer, about 10 to 12 minutes more depending on the desired temperature. (The risk of error is high with handheld thermometer styles, so be sure to use a clip-on.) For more delicate caramel notes and a cleaner hazelnut flavor, stop at the low end of that range; for a bolder, bittersweet flavor, aim for the higher end of the range.

Remove from heat, then immediately stir in baking soda, folding with the heat-resistant spatula until the candy is evenly foamy, then pour onto the prepared sheet pan. Cool to room temperature, then proceed immediately to the next step. If the candy is allowed to sit out for extended periods of time after cooling, it will turn tacky and soft. Alternatively, wrap the cooled candy tightly in plastic and store in an airtight container for up to 1 week at cool room temperature or for several months in the fridge or freezer.

To Make the Chocolate-Hazelnut Spread: Break the brittle into pieces and transfer to the bowl of a food processor. Pulse several times to pulverize the candy, then let food processor run continuously until the brittle transforms into a thick, peanut butter–like paste. This typically takes between 3 and 5 minutes, but that range can vary substantially depending on the size and power of the machine.

Add cocoa powder and process until well distributed. With the machine still running, pour in melted chocolate, along with roasted hazelnut oil. Scrape the blade and bowl, particularly around the bottom and in the corners, then continue processing until homogeneous and relatively smooth.

Transfer to an airtight container and store up to 1 month at cool room temperature or several months in the fridge. When freshly made, the mixture will be loose-bodied, with a tacky texture from the warm candy bits. As the spread cools, its texture will become delicately crisp; the spread will set with a firm, truffle-like consistency over the course of 24 to 36 hours at cool room temperature. This mixture can be used as a cookie filling or truffle center, as a crispy ice cream swirl , or as a spread for toast, crepes , and French toast .