Ingredients

• 3-1/2  cups all-purpose flour
• 2/3  cup unsweetened Dutch-process cocoa powder or unsweetened cocoa powder
• 2  teaspoons baking powder
• 1-1/3  cups butter, softened
• 1-1/2  cups sugar
• 1/4  cup cooking oil
• 2  eggs
• 1  tablespoon vanilla
•   Sugar
• 1  14-ounce can sweetened condensed milk
• 1  10-ounce package mint-flavor semisweet chocolate pieces*
• 2  ounces unsweetened chocolate, coarsely chopped

Directions

1. In a medium bowl, combine flour, cocoa powder, and baking powder; set aside.

2. In a large bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add the 1-1/2 cups sugar and the oil. Beat until well mixed. Add eggs and vanilla; beat until combined. Add flour mixture; beat until combined. Cover and chill about 1 hour or until dough is easy to handle.

3. Preheat oven to 350 degrees F. Shape dough into 1-inch balls. Place balls 2 inches apart on an ungreased cookie sheet. Dip the bottom of a glass in additional sugar and flatten each cookie. Bake in preheated oven for 7 to 9 minutes or just until firm. Transfer cookies to a wire rack; let cool.

4. For filling: In a small saucepan, combine sweetened condensed milk, chocolate pieces, and unsweetened chocolate. Cook and stir over medium heat until melted and smooth. Remove from heat. Let stand about 1 hour or until cool.

5. Spoon a rounded measuring teaspoon of the filling on the bottom of each of half of the cookies. Top with remaining cookies, flat sides down, pressing lightly together. Makes about 36 sandwich cookies.

6. *Test Kitchen Tip: If you can't find mint-flavor semisweet chocolate pieces, use 1 1/2 cups regular semisweet chocolate pieces and stir 1/4 teaspoon mint extract into the melted chocolate mixture.

7. To Store: Place filled cookies in a single layer in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months.