Preheat oven to 350 degrees. Line an 8-inch square baking pan with parchment, leaving a 2-inch overhang on 2 sides.
Cream butter, vanilla seeds, and sugar with a mixer until fluffy. Reduce speed to low; add flour, hazelnuts, and salt. Press into pan; freeze until firm, about 30 minutes. Score shortbread into 18 pieces; bake until gold, 55 to 60 minutes. Let cool for 15 minutes; unmold using overhang. Let cool on a wire rack. Cut into pieces. Shortbread will keep, covered, for up to 3 days.
Brown-rice (#1460C24), $3.03 for 24 oz.; almond (#4999C16), $12.17 for 16 oz.; and quinoa (#1448C22), $11.22 for 22 oz.; from Bob's Red Mill, 800-349-2173 bobsredmill.com.