1. Cookies: Preheat oven to 350°F (175°C). In a large bowl, beat butter and sugar until smooth. Add eggs and vanilla, beating well. Stir in flour, baking powder, and salt. Mix until dough forms. Shape dough into balls and place on baking sheet. Flatten slightly. Bake 10-12 minutes. Let cool.
2. Cream Filling: In a saucepan, mix milk, sugar, cornstarch, and salt. Cook over medium heat, stirring constantly, until thickened. In a small bowl, beat egg yolks. Add a little of the hot mixture to the yolks, then return to saucepan. Cook 2 more minutes. Remove from heat and stir in vanilla. Let cool.

3. Chocolate Frosting: In a bowl, microwave chocolate chips and heavy cream in 30-second intervals, stirring between each, until smooth.
4. Assembly: Place a spoonful of the cream filling on one cookie and top with another cookie. Dip top into chocolate frosting. Let cool until chocolate is firm.

Total Time: 1 hour
Servings: 24 bites