Cream the butter and two sugars until light and fluffy in the bowl of an electric mixer fitted with the paddle attachment. Add the vanilla, then the eggs one at a time, and mix well. Add the cocoa and mix again. Sift together the flour, baking soda, and salt and add to the chocolate with the mixer on low speed until just combined.
Drop the dough on a baking sheet lined with parchment paper, using a 1 3/4 inch ice cream scoop or a rounded tablespoon. Dampen your hands and flatten the dough slightly. Bake for exactly 15 minutes (the cookies will seem underdone). Remove from the oven and let cool slightly on the pan, then transfer to a wire rack to cool completely.
To prepare the topping & decorate:
In a double boiler, slowly melt the white chocolate chips. You may need to add a splash of milk here or there to keep it from seizing. I added about a tablespoon to mine to keep it the right consistency. With a small frosting spatula or butter knife, spread a nice layer of chocolate on each cookie. Careful to not burn your fingers.
The chocolate will cool quickly so have your children decorate the cookies 1 at a time as you hand them over. Though the chocolate was hot to touch while I spread it on the cookie, my girls had no problems with it. Please just warn your helpers to just sprinkle the decorations and not handle the hot cookies till they’ve cooled just to be safe.
Recipe adapted from Barefoot Contessa Parties! decoration idea adapted from Annie’s Eats