How to Make It
Sift the rice flour with the cornstarch into a medium bowl. In a stand mixer fitted with the paddle, beat the clarified butter with the confectioners’ sugar at medium speed until smooth, about 1 minute. At low speed, beat in the egg yolks one at a time, then gradually add the rosewater until incorporated. Add the dry ingredients and beat at low speed until smooth. Scrape the dough into a medium bowl, press a piece of plastic wrap directly on the surface and refrigerate until just firm, about 1 hour.
Preheat the oven to 350°. Line 3 large baking sheets with parchment paper. Scoop tablespoon-size mounds of the cookie dough onto the baking sheets. Roll the mounds into balls, then gently press them 1/2 inch thick. Using the wide end of a thimble, gently press 3 slightly overlapping rings onto each round. Sprinkle the center of each cookie with poppy seeds.
Bake the cookies for about 18 minutes, until they are firm and just starting to color on the bottom. Let cool completely, about 45 minutes. Using a thin metal spatula, transfer the cookies to a platter and serve.
Using a high-quality, pure rosewater is essential here. Look for Sadaf brand, which is available at kalustyans.com.
To make clarified butter, melt 1 pound of butter over low heat. Remove from the heat and skim off the foam. Using a ladle, remove the clear melted butter, leaving the milky white solids behind; discard the solids. Refrigerate the clarified butter until solidified but not hard, about 30 minutes.