In a medium bowl, whisk together 2 cups (240 grams) confectioners’ sugar and 3 tablespoons plus 1 teaspoon (50 grams) water until smooth. Add remaining ½ cup (60 grams) confectioners’ sugar, and whisk until combined. Tap bowl on a kitchen towel-lined counter to remove any air bubbles from surface. Dip tops of Oatmeal Cookies in glaze, letting excess drip off. Let stand until glaze is set.