In a medium bowl, whisk the flour, baking powder, and salt.
In a stand mixer, beat butter on medium speed until smooth, about 1 minute. Add 1 1/2 cups of the sugar and the vanilla and beat on medium speed until well blended, about 2 minutes. Add the eggs and yolks one at a time, mixing until blended after each addition. Add the flour mixture and mix on low speed until just blended, about 1 minute.
Turn the dough out onto a large piece of plastic wrap. Using the plastic wrap as an aid, gently knead into a smooth dough (the dough will be soft). Shape into a 12" round log about 3" in diameter and wrap in the plastic. Cut an empty paper towel roll open. Gently rest the dough in the roll and refrigerate until chilled and very firm, about 4 hours and up to 3 days. Dough can be frozen for up to one month.
Preheat oven to 350 degrees. Line 2 or more cookie sheets with parchment paper or nonstick baking liners. Put remaining 1/3 cup sugar in a small bowl.
Cut the dough into 1/4" slices. Gently press one side of cookie into the sugar to coat completely. Arrange the cookies sugar side up about 1" apart on the cookies sheets. Save the rest of the sugar for decorating the cookies. Bake, one sheet at a time, until golden brown, about 11-14 minutes. Let cookies cool on sheets for about 5 minute, then transfer to a rack for cool completely. Cookies may be stored in an airtight container at room temperature for up to 3 days before proceeding.
Dip sugared side of the cookies into the remaining sugar. Arrange cookies sugar side up on a flameprrof work surface. Pass the flame of a small kitchen torch over the cookies tops until evenly carmelized. Let cool completely before serving.