Preheat the fan-assisted oven to 170°C / 340°C or a regular oven to 180°C / 350°C. Line a 30 cm x 40 cm (or 12-inch x 16-inch) baking sheet with parchment paper.
Combine all-purpose flour, ground almonds, sugar, and diced tarragon in a bowl. Cut the cold butter into small cubes and add to the dry ingredients. Using your fingertips, lightly rub the butter into the mixture to get a sand-like texture, then knead it together to combine. Refrain from overworking the mixture. Grate the mixture over the prepared baking sheet. Place in the oven and bake for 15 - 20 minutes or until golden brown and crunchy. Cool, and keep in an airtight container at room temperature until needed.