• Preheat oven to 350℉.
• Place 1 cup of the semi-sweet chocolate chips in a plastic bag and use a rolling pin to break them down into small pieces (set the other 1 cup of unchopped chocolate chips aside).
• In a small microwave-safe bowl, melt the unsalted butter (1 cup, i.e. 2 sticks) for 20-30 seconds until JUST melted. 
• Add in granulated sugar (½ cup) and light brown sugar (1 cup) and use a spatula to stir until combined (* do not use a mixer!*). Add in eggs (2 large) and vanilla extract (1 tablespoon), then mix. Next, add in baking soda (1 teaspoon), baking powder (½ teaspoon), and salt (½ teaspoon) and mix again. Add in all-purpose flour (3 cups) and mix until all the flour disappears into the dough.
• Add the 1 cup of chopped chocolate chips and 1 cup of whole chocolate chips into the dough and mix.  Immediately proceed to pressing into pan (you don't want the dough sitting out or it will set too much with the melted butter).
• Grease (2) 8-inch round cake pans and line bottom with parchment paper (see notes below for alternate pans). Divide dough among the two pans and press into an even layer.
• Bake at 350℉ for 22-26 minutes or until cookie is lightly golden brown. While cookies are baking, make frosting.
• Allow to cool completely. Run a knife along the edges to loosen, then invert onto a cookie sheet or cooling rack.

To decorate:

• Place one of the cookies upside down onto your serving platter (for the bottom layer, we want the flat edge to be on top).
• Using a knife or large star piping tip, spread or pipe two-thirds of the frosting onto the bottom layer. Once smooth, place the remaining cookie on top (as shown in the photos in the post above). Use your remaining frosting and a large star piping tip to pipe around the edges, then add sprinkles.

To Make Frosting:

• Beat the softened unsalted butter (¾ cup, i.e. 1 ½ sticks butter) on medium-high speed for 2-minutes until smooth. Turn the mixer to low speed then add the powdered sugar ¼ cup at a time (3 ¾ cups total). You may need to stop and scrape down sides. Add vanilla extract (1 tablespoon) and salt (¼ teaspoon) and turn mixer to medium speed. One tablespoon at a time, add milk (3 tablespoons total). Beat on high for 2-3 minutes until creamy and the frosting is at a good consistency to pipe. If it looks too runny, add more powdered sugar. If it looks too stiff, add a tiny bit of milk until you get to the desired consistency.

  This will make just enough frosting to pipe a border along the edges, as well as write a phrase on top.