Melt in your Mouth Sandwich Cookies

Directions

1. Position a rack in the middle of the oven. Heat oven to 300 degrees F. Line two baking sheets with parchment paper.
2. Into a medium-sized bowl, sift both flours, cornstarch, baking powder and salt and set aside.
3. In a large bowl and using an electric mixer on medium speed, beat the butter, sugar and vanilla until smooth and lightened slightly in color, 1 minute. Stop the mixer and scrape the sides of the bowl as needed during the mixing.
4. Mix in the flour mixture just until the flour is incorporated and a smooth dough forms.
5. For each cookie, roll a level tablespoon of dough between the palms of your hands into a smooth ball. Place the cookies on the prepared baking sheets, spacing them 2 inches apart.
6. Use a fork to gently flatten the cookies to 1-1/4-inch disks and to make an impression of the fork tines in the top of each.
7. Bake the cookies one sheet at a time until the tops feel firm but do not darken, about 30 minutes or just set.
8. Transfer the cookies to a wire rack to cool completely.
9. In a second medium-sized bowl, mix butter, sugar and vanilla until smooth. Stir in melted chocolate.
10. Turn half of the cooled cookies bottom side up. Use a thin metal spatula to spread a rounded teaspoon of filling evenly over bottom of each.
11. Gently press the flat bottom of the remaining cookies on the filling. Serve at room temperature.