Melt the chocolate in the microwave at 20-second intervals and stir the chocolate after each round. You can melt the chocolate in a double boiler. Let the chocolate cool down.
50 grams Semi-sweet chocolate
Use the paddle attachment to beat the butter and sugar until well blended. Scrape the bowl as needed.
½ cup Butter, 1 cup+1tbsp Granulated sugar
Add the egg, yolk, and vanilla extract. Mix well.
1 Egg, 1 Yolk, 1 teaspoon Vanilla extract
Add in the melted chocolate and mix well.
Sift the AP flour, whole wheat, baking powder, cocoa powder, and salt. Add this to the butter mixture and mix well.
1¼ cup All-purpose flour, ¼ cup Whole wheat flour, 1 tablespoon Cocoa powder, ¾ teaspoon Baking powder, ¼ teaspoon Salt
Shape the cookie dough into a rectangular shape, wrap it tightly separately in cling wrap, and chill it for at least an hour.
Preheat the oven to 350℉ and line a baking sheet with parchment paper. Set it aside.
Use an ice cream scoop or your clean hands to make small balls the size of a walnut in its shell. Place the dough ball on the baking sheet and press its center with a one-teaspoon Round Measuring Spoon to make a round indentation. Bake the cookies for 8-10 minutes, and immediately after removing them from the oven, soften the edges with the back of a spoon to make them look as round as possible. The indentations will puff up and almost disappear. While the cookies are still hot, press their center with the same round teaspoon to make them deep enough to fill up with chocolate ganache.
Let the cookies cool down completely, and move on to making the chocolate ganache!