- With the rack in the middle position, preheat the oven to 400 °F (200 °C). Line two baking sheets paper parchment or silicone mats.
- In a bowl, cream the butter, brown sugar and salt with an electric mixer. Add the egg and beat until smooth. With a wooden spoon, stir in the flour and hazelnuts.
- Spread the batter at the bottom of the bowl. With a spoon, drizzle the hazelnut spread randomly over the dough. Do not stir to maintain a marbled effect.
- With a 2 tbsp (30 ml ) ice cream scoop, shape dough balls. Place on the prepared sheets, spacing them evenly. Freeze at this stage if desired. Then place the frozen cookies in sealable plastic bags and keep in the freezer until ready to bake. They will keep for about 3 months.
- Bake, one sheet at a time, for about 8 minutes or until the cookies are firm around the edges, but still soft in the centre. Let cool completely on the sheet.