The deep hazelnut flavor and buttery goodness of these cookies belie their simplicity. With just five ingredients, these are some of the easiest cookies to make. Martha made this recipe on episode 704 of Martha Bakes.
Preheat oven to 375 degrees. Place hazelnuts on a baking sheet and toast until golden and fragrant, 10 to 15 minutes. Remove from oven and let cool completely. Reduce oven temperature to 350 degrees. Pulse in a food processor until just finely ground (do not grind into a paste).
In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar until light and fluffy, 2 to 3 minutes. Add flour, ground hazelnuts, and salt; beat until dough forms. If needed, drizzle in 1 to 2 tablespoons water, 1 tablespoon at a time, to help form a dough. Dough can be wrapped well in plastic and refrigerated up to 1 day or frozen up to 3 months (thaw in refrigerator before using).
Roll dough into 1-inch balls and transfer to parchment-lined baking sheets, spacing 2 inches apart. Press balls with tines of fork to flatten. Bake until edges are golden, rotating sheets halfway through, 12 to 15 minutes. Transfer sheets to a wire rack and let cookies cool completely. Cookies can be stored in an airtight container at room temperature up to 3 days.
You can also use store-bought hazelnut meal instead of grinding whole nuts.