In a large bowl, combine the butter, confectioners' sugar, and granulated sugar. Beat at medium speed with an electric mixer until fluffy. Beat in the egg and vanilla. Gradually add the chocolate to the butter mixture, beating until combined.
In a medium bowl, combine the flour and baking soda. Gradually add to the sugar mixture, beating until combined. Divide the dough in half. Press each half into a 10-inch disk, wrap in heavy-duty plastic wrap, and chill 1 hour.
Preheat the oven to 350 degrees F. Line baking sheets with parchment paper.
On a lightly floured surface, roll out the dough to 1/4-inch thickness. Using a 2 1/2-inch flower shaped cutter, cut out the dough. Place 1 inch apart on prepared baking sheets. Bake for 10 minutes. Let cool on the pan for 2 minutes. Remove from the pan, and cool completely on wire racks. Pipe or spoon Cream Cheese Flower Center Frosting onto center of each cookie. Sprinkle with sprinkles or sanding sugar, if desired.
In a medium bowl, combine the cream cheese and butter. Beat at medium speed with an electric mixer until creamy. Gradually beat in confectioners' sugar until smooth.