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PRE-HEAT your oven to 350 degrees Fahrenheit or 180 degrees Celsius. SIFT flour, salt and cocoa powder in a small bowl. MIX together well. PUT the butter along with the sugar to the stand mixer's bowl.
CREAM until the mixture gets pale and fluffy, then reduce speed to medium. ADD two egg yolks and beat in the flour and cocoa mixture until a nice cookie dough forms. ROLL small balls (about 2 teaspoons full) using the dough and roll each ball in sugar.
We just added sugar to our kitchen counter, but you can use a bowl for this if you don't want too much mess. PLACE them on the pre-lined baking sheet about 1 inch (2.5 cm) apart. They won't expand too much, but leave some space in between.
USE your thumb to press small indentations in the middle of each sugared cookie dough ball.
BAKE the cookies for about 10 to 15 minutes, or until the cookies are just set. If the cookie indentations loose definition, use your thumb to re-create these centers again.
After baking, let the cookies cool off to room temperature. It's best to use a wire cooling rack for this.
Very easy, just combine 1:1 ratio heavy cream and unsalted dark chocolate in a small saucepan. Let the cream get warm first, then add in the chocolate. FINELY chop the chocolate first, if you are using chocolate bars.
Finish these cookies with a nice ganache. Fill each cavity with a small amount of ganache and let stand until cooled off. These cookies cannot be stacked without creating a mess. You can keep these for about 3 days when covered properly.
Enjoy these chocolate thumbprint cookies with a nice cup of tea or coffee.