In large bowl, beat butter, eggs, and vanilla with electric mixer at medium speed until well combined. With electric mixer on low speed, add flour mixture to egg mixture 1 cup at a time, scraping bottom and sides of bowl as needed. Mix until just combined. Beat in hazelnuts. On lightly floured surface, pat into a 10 in. x 2 in. X 1 in. log; place in middle of prepared cookie sheet.