Step 1

Preheat oven to 350°.

Step 2

Weigh or lightly spoon flour and potato starch into dry measuring cups; level with a knife. Combine flour, potato starch, and next 4 ingredients (through salt) in a medium bowl, stirring with a whisk.

Step 3

Place butter, brown sugar, and granulated sugar in a large bowl; beat with a mixer at medium speed until blended. Add corn syrup, vanilla, and egg yolks, beating at low speed. Add flour mixture; beat at low speed until blended.

Step 4

Combine turbinado sugar and cinnamon in a small bowl. Shape dough with moist hands into 1-inch balls. Roll balls in sugar mixture. Place 2 inches apart on a baking sheet lined with parchment paper; flatten cookies with the bottom of a glass. Bake at 350° for 8 to 10 minutes or until edges of cookies are golden brown. Cool completely on pan.