vegetarianRoast the hazelnuts
Spread the Hazelnuts (chopped and roasted) on a small baking tray in an even layer and toast them in the oven at 350° F for about 8 minutes, stirring once halfway through, until they smell nutty and look lightly golden. Let them cool, then give them a rough chop so you have small pieces for the coating later.
Portion the filling
Line a tray or plate with little squares of cling film or baking paper. Spoon small 1/2-teaspoon mounds of Nutella (or hazelnut spread) onto the lined tray, then wrap each one up so it holds a compact little blob. Freeze the filling pieces until firm enough to handle easily.
Cream butter and sugars
In a large mixing bowl, beat the Unsalted Butter (cold, chopped) with a mixer until it starts to smooth out. Add the Caster Sugar and Light Brown Sugar, then beat for a few minutes until the mixture looks lighter, fluffier, and creamy rather than dense.
Add egg and vanilla
Crack in the Egg (whole), add the Egg Yolk, and pour in the Vanilla. Mix just until the wet ingredients are fully incorporated and the mixture looks smooth and glossy.
Mix the dry ingredients
Add the Plain Flour, Salt, Baking Powder, and Baking Soda to the bowl. Stir on low speed or fold with a spatula just until no dry streaks remain and you have a soft cookie dough.
Shape stuffed cookies
Divide the dough into portions of about 65 to 70 g each. Flatten one piece in your hand, place a frozen Nutella centre in the middle, and wrap the dough up and around it. Pinch the seams closed well, then roll it gently into a smooth ball. Repeat with the remaining dough and filling.
Freeze the dough balls
Arrange the stuffed cookie dough balls on a tray, leaving a little space between them, and freeze until very firm. This helps them keep a thick shape in the oven and gives you that soft centre.
Preheat the oven
Heat the oven to 350° F so it is fully ready by the time the dough balls are firm.
Bake the cookies
Place the frozen dough balls on lined baking trays with enough room for spreading. Bake for 10 minutes, then keep checking until the tops are lightly golden and the edges look set but the centres still seem a little soft, usually up to about 15 minutes total. Leave them on the tray for a few minutes so they can finish setting before moving them to a rack to cool completely.
Melt the chocolate
Finely chop the Chocolate (cooking or milk) if it is in large pieces. Put it in a heatproof bowl over a pan of barely simmering water and stir until melted and smooth. Take the bowl off the heat, then stir in the chopped roasted hazelnuts until everything is evenly coated.
Coat the cookies
Set a sheet of baking paper on a tray or work surface. Spoon a thin round of the chocolate-hazelnut mixture slightly larger than the base of one cooled cookie, place the cookie on top, then spoon more chocolate mixture over and around it to coat. Repeat with the remaining cookies.
Let them set
Leave the coated cookies at room temperature until the chocolate is firm, or chill them briefly if your kitchen is warm. Serve once the coating is fully set and crisp.
