Preheat oven to 350°F. Line a cookie sheet with parchment paper. Set aside.

In a large bowl, sift together flour, cornstarch, salt, and baking powder. Mix and set aside.

Place butter and sugar in large bowl of electric stand mixer and beat on medium speed until light in color. Add vanilla and milk and beat to combine. Add the flan mix and beat until well incorporated. Put mixer on low speed, gradually add flour mixture, and beat until mixture pulls away from the side of the bowl.

Roll dough into 1-inch balls. Place balls 2 inches apart on prepared cookie sheets.

Bake for 10 to 12 minutes. Cool on wire rack.

Store in airtight container for up to 1 week.