If you have walnut oil on hand, taste it first to make sure it's fresh. You don't want any off-flavors in these delicate cookies.
MAKE AHEAD: The cookies can be stored at room temperature for 5 days; after that, they might start to become more chewy than crisp. But they'll still taste good.
Makes about 48 cookies
Position the oven racks in the upper and lower thirds of the oven; preheat to 350 degrees. Line 2 large baking sheets with parchment paper or silicone liners.
Even if you're using roasted sesame seeds, toast them in a small, dry, heavy-bottomed skillet over medium heat until lightly browned and/or fragrant. Cool for a few minutes, then stir in the poppy seeds.
Combine the butter and sugar in the bowl of a stand mixer or hand-held electric mixer. Beat on low speed until smooth, then on medium speed until fluffy. Stop to scrape down the sides of the bowl. Add the egg whites in thirds, beating on low speed to incorporate after each addition and stopping to scrape down the bowl as needed. Add the flour; beat (on low speed) until just combined.
Stir in the walnut oil by hand. Transfer half of the batter to a piping bag fitted with a 1/2-inch plain round tip. (The remaining batter can stay at room temperature.) Pipe out 1 1/2-inch-wide disks on each baking sheet, spacing them 1 1/2 inches apart. (Alternatively, you can use a spoon to do that.) Bake on the upper and lower racks for about 7 minutes, then rotate the baking sheets top to bottom and front to back. Bake for about 8 minutes or until the cookies are just lightly browned on the edges.
Transfer the sheets to the stove top (off the heat) and let them sit for 5 minutes, then transfer the cookies to a wire rack to cool completely before serving or storing. Repeat to use all of the batter.
Recipe Source:
From chef-restaurateur Michel Richard of Michel Richard Citronelle and Central.
50 calories, 2g fat, 1g saturated fat, 5mg cholesterol, 5mg sodium, 8g carbohydrates, 0g dietary fiber, 5g sugar, 0g protein.