01 -
Whisk together all-purpose flour, Dutch process cocoa powder, salt, and baking powder in a medium bowl until combined.
02 -
Using an electric mixer, cream softened unsalted butter with light brown and granulated sugars for about two minutes until smooth and fluffy.
03 -
Add egg yolks and vanilla bean paste or extract to the butter mixture; beat for 1 to 2 minutes until pale and fluffy.
04 -
Gradually add dry ingredients to wet mixture and mix just until combined, avoiding overmixing to maintain tenderness.
05 -
Scoop approximately 1 tablespoon of dough per cookie (total 34). Roll into balls and place on parchment-lined baking sheets. Press a 1/4 teaspoon-sized indent into the center of each ball.
06 -
Refrigerate the indent-pressed dough balls on baking sheets for at least one hour before baking.
07 -
Set oven temperature to 350°F (175°C).
08 -
Arrange dough balls 1 1/2 inches apart and bake for 10 minutes, until edges are set.
09 -
Immediately after baking, gently press centers again with 1/4 teaspoon measure to deepen thumbprints if necessary, smoothing edges with a cookie cutter while warm.
10 -
Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
11 -
Heat heavy cream until just boiling, pour over semi-sweet chocolate chips, let sit for 1 minute, then stir gently until smooth.
12 -
Spoon approximately 1 teaspoon of ganache into each cookie indentation and decorate with nonpareils if desired.
13 -
Chill cookies in the refrigerator for 10 to 15 minutes to allow ganache to firm.