Line several rimmed baking sheets with parchment paper.
In a medium bowl, combine hazelnut flour and salt, whisking well.
In a large mixing bowl, combine butter and sugar, beating at high speed with a mixer until light and creamy, approximately 3 minutes. Add egg yolks and vanilla extract, beating until incorporated. Add hazelnut mixture to butter mixture, beating until incorporated.
Using a levered 1-teaspoon scoop, drop batter 3 inches apart onto prepared baking sheets.
Bake until cookie edges are golden brown, approximately 10 minutes. Let cool on baking sheets for 1 minute. Transfer cookies to wire cooling racks, and let cool completely.
Store at room temperature in an airtight container with layers separated by wax paper for up to 3 days.
Recipe by TeaTime Magazine at https://teatimemagazine.com/hazelnut-wafer-cookies-recipe/