Preheat oven to 350 degrees Fahrenheit.
Cream butter and sugar until the butter is pale in color, about 2 minutes in a stand-mixer. Add in egg yolk and vanilla until everything is well incorporated.
Sift the cocoa powder and flour before measuring. Use a knife to make level measurements of both, and add each to a medium sized bowl. Add the salt, and whisk all the ingredients together.
Add the dry mixture to the wet ingredients, and mix until everything is incorporated, scraping down the sides of the mixer bowl.
Line two baking sheets with parchment paper or silicon mat. Form the dough into 1" balls, and roll in granulated sugar. Place on baking sheet, and use your finger to make a depression in the cookie. Don't depress so much that you end up touching the baking sheet.
Bake in the oven for 10 - 12 minutes.
Remove from the oven, and depress the cookies again. Sometimes in the cooking process, the thumbprint will raise a bit.
Immediately remove to a wire rack to cool.
Heat the cream in a small saucepan over medium heat until you see bubbles forming around the edges of the pot. Do not let the cream come to a boil.
Add the chocolate chips to a small bowl. Pour the hot cream over the chocolate chips, and let sit for one minute. Using a whisk, mix the cream and chocolate chips together until smooth.
Place one dried bing cherry in each of the depressions of the thumbprint cookies. Top with 1 teaspoon ganache, so that the cherry is completely covered, and the ganache touches the actual cookie. You want to cover the cherry completely, and have it secure in the cookie, so it remains a surprise for the recipient!