Beat butter and sugar until fluffy. Add egg and vanilla.
Whisk flour, baking powder, and salt. Fold into butter mixture.
Divide and roll each portion between parchment into ¼-inch rectangles.
Combine jam and cornstarch in a small bowl.
Spread jam evenly, roll tightly, and wrap in plastic wrap.
Refrigerate logs for 2 hours or freeze for 30 minutes.
Slice ½-inch thick rounds, bake at 350°F for 10–12 minutes.
Let cookies cool before transferring to a container.
