Heat the oven to 350°F and arrange a rack in the middle. Combine butter, sugar, and cream cheese in the bowl of a stand mixer fitted with the paddle attachment and mix on medium until light and fluffy, about 2 minutes. Scrape down the bowl sides and bottom. Add egg yolk, vanilla, and salt and beat until smooth, about 30 seconds. Add flour and mix on low until the dough comes together. Place dough in a piping bag fitted with a star tip, squeezing the dough toward the tip of the bag to eliminate air pockets. Twist the bag down tightly on the cookie dough and hold the bag at the point where you started the twist—this will be your squeezing hand. Use your other hand to guide the tip. Hold the bag perpendicular to a baking sheet, aiming the tip where you want the center of the cookie to be. Squeezing firmly on the bag’s end, pipe the cookies by guiding the bag in a counterclockwise spiral out from the cookie’s center. Make only one full rotation, and try to keep the spiral as tight as possible. With the end of a wooden spoon, make an indentation about 1/2 inch wide and 1/2 inch deep in the center of each spiral; dip the spoon handle in flour if it sticks to the cookie dough. Place the jam in a resealable plastic bag and squeeze it into one corner. Cut a 1/4-inch piece off the corner. Pipe enough jam into each cookie indentation to fully fill; don’t overfill or the jam will run out onto the cookie. Bake cookies until the edges are golden brown, about 15 to 20 minutes. Let cookies sit on the baking sheet for 5 minutes before removing to a rack to cool.