Preheat oven to 350 degrees. Line two cookie sheets with parchment paper or a silicone baking mat and set aside.
In a medium to large bowl cream together the butter, shortening and brown sugar on medium- high speed for 2 minutes or until light and fluffy. Add the egg yolks, cream, vanilla and salt, and beat until well combined; occasionally scraping down the sides. Gradually add the flour, mixing on low until well combined.
Using a cookie scoop (about 2 -3 tablespoons), scoop out dough and roll into balls. Place the rolled dough balls in the sugar to coat. Using the back of the cookie scoop (or your fingers) make a well in the top middle of each ball.
Bake for approximately 10 minutes, then remove from oven. Place approximately 1 teaspoon jam, jelly or preserves into the well of each cookie. Bake for an additional 5 to 10 minutes, or until lightly browned. Remove from oven and cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
Recipe by jessica burns at http://jessicaburns.com/2015/02/berry-thumbprint-cookies/