Cream the butter and sugar in a large bowl with an electric mixer until smooth. Add the sugar, egg yolks, vanilla, lemon zest, lemon juice, baking powder, salt and flour. Mix on low speed until combined.
Cover and refrigerate dough for at least one hour.
When you're ready to bake, preheat the oven to 350 degrees. Line two baking sheets with parchment paper or silpat mat.
Very generously flour a work surface.
Scoop a palm-sized chunk of cookie dough from the bowl and place on the floured surface -- leaving the bowl of dough in the refrigerator to continue to chill.
Sprinkle flour on top of the dough and quickly roll out the dough to about 1/4" thick, making sure that the dough isn't stuck to the work surface. Dough is very soft and has a tendency to stick. (I rolled the dough once in each direction, then lifted it -- refloured the work surface and flipped the dough over onto the flour to continue to roll.)
Dip your cookie cutter into flour so it doesn't stick to dough. Press cookie cutter into dough and transfer to baking sheet. If they stick to the work surface, use more flour when rolling them out. You can also use an off-set spatula, dipped in flour to lift the cookies and transfer them to the cookie sheet.
Sprinkle with one of the sugars or poppy seeds and lightly press them into the dough with your fingers.
Bake for 8-10 minutes until lightly browned. Transfer to a rack to cool.
To melt chocolate, place chocolate chips or chunks in a clean glass bowl. Place the bowl in a microwave and heat in 10 second intervals at 50% power, stirring after each nuking. Do not heat on high or for extended time, otherwise your chocolate may seize. (Ask me how I know.)
When the chocolate is smooth and melted, transfer it to a resealable plastic sandwich baggie and trim a tiny corner off the end. "Pipe" the chocolate over the cookies. Let the chocolate harden before storing them in an airtight container, separating each layer with a piece of parchment paper.
NOTE: Use as small a cookie cutter as you can for these. Your yield will be higher or lower depending on the size of cookie cutter you use. I recommend a very small one - about 1 1/2" or smaller.