In a large bowl, whisk together butter, sugar, vanilla extract, and egg yolk.
As soon as the mixture is smooth, add baking powder and flour in small portions. Mix together with a spatula or by hand. Dough will be a bit crumbly but that is perfectly OK.
Using a standing mixer, beat together egg whites with sugar on high until you get stiff peaks. This should take about 10 minutes.
Break off a part of the dough, cover it with plastic wrap and roll it out to 1/4 of an inch thickness.
Using a cookie cutter, cut out the size of cookies based on your preference. Use a knife to lift each cookie onto a baking sheet.
Place a tip inside a piping bag. Using a toothpick draw a line of color on the inside. Pipe out a shape of your preference on top of each cookie.
Bake cookies at 200°F for about 2 hours. To check if the meringue is baked, tap it with a spoon to see if they make a hollow sound. Stick two cookies together by placing jam in the middle.