Lightly brown the butter. See notes*
½ cup Butter
using he paddle attachment beat the cool butter with two sugars until well mixed.
1 cup Brown sugar, ¼ cup Granulated sugar
Add the egg, yolk, and vanilla extract. Beat the mixture for two minutes until light brown and smooth.
1 Egg, 1 Yolk, 2 teaspoon Vanilla extract
In a separate bowl, measure the flour, then remove one tablespoon of it and replace it with whole wheat flour. Whisk all dry ingredients and add them to the above mixture in two batches. Stop mixing when there is no trace of dry flour. Use a rubber spatula to mix everything.
1¾ cup - 1 tablespoon All-purpose flour, 1 teaspoon Cornstarch, 1 tablespoon Whole wheat flour, ¾ teaspoon Baking soda, ¼ teaspoon Salt
Cover the dough and chill it for at least an hour.
Preheat the oven to 350℉, and line two baking sheets with parchment paper.
Scoop the dough into small balls the size of a shelled walnut. Place them on the lined baking sheets. Leave two inches of space between them.
Bake them for 10-12 minutes or until the edges are set and slightly golden.
Let them cool down on the baking sheet for 8-9 minutes, then transfer them to the cooling rack to cool down completely.