In a large mixing bowl, place 3 egg whites, ¼ teaspoon cream of tartar, 1 ¼ teaspoons vanilla extract, and a dash of salt. Beat on high speed with an electric mixer until foamy. Gradually add sugar, continually beating until stiff peaks form and sugar is dissolved. Spoon the mixture into a zip-lock plastic bag. Snip one bottom corner of the bag to make a hole that is 1-inch across. Pipe mixture into 1 ¼-inch mounds onto a parchment paper-lined baking pan. Bake at 200 degrees (F) for 2 hours. Remove from oven and cool completely (about 30 minutes). When meringue mounds are cooled completely, place 4 ounces of milk chocolate chips in the top of a double boiler. Bring the water below to a boil and stir chocolate constantly until melted. Turn off heat. Spread a thin layer of melted milk chocolate onto half of the flat sides of the meringue mounds. Gently press flat sides of remaining half of meringue rounds onto chocolate-covered side of meringue mounds. Let stand until chocolate is set (about an hour). Place Chocolate-Filled Meringue Sandwich Cookies on a nice serving tray. These are a great treat for a party. With the Playoffs and Super Bowl games coming up, this is a sweet treat that you might like to serve. It is quick, easy, and impressive. It is wonderful for any get-together or just for a comfort snack at home. Enjoy!!! --Betty