In a stand mixer or a medium or large bowl with a hand mixer, combine the softened butter and cream cheese.
Right over the same bowl (if using a hand or tilt head mixer) or over a separate medium bowl (if using a bowl-lift mixer), sift the powdered sugar. Add the powdered sugar in a few batches and start the mixer on a low speed to incorporate the powdered sugar before you add more.
Add salt and vanilla and mix in then increase the mixer to medium-high speed for 3-5 minutes until fluffy and lighter in color.
Prepare a piping bag with a medium round tip (Wilton 12 or equivalent) and fill with prepared frosting. Set aside.
Place strawberry jam in a small bowl and whisk with a small whisk or fork until it has loosened up and is thin enough to pipe.
Prepare a piping bag with a small round tip (Wilton 10 or equivalent) and fill with prepared jam. Set aside.
With frosting, begin to make a swirl on each cookie, starting on the edge of the cookie and working your way to the center, leaving space between each frosting swirl for the jam swirl.
Next, pipe a thinner swirl of jam in the empty space on each cookie, alongside the frosting swirl.
Optional: Smooth out any chunky-looking jam spots with a toothpick.