Preheat your oven to 325°F (160°C) and line baking sheets with parchment paper.

In a stand mixer, combine unsalted butter, icing sugar, salt, and vanilla extract. Beat on medium speed for about 3 minutes until fluffy.

Gradually add all-purpose flour, mixing on low speed until the dough forms a ball.

Transfer the dough to a floured surface, knead gently, wrap in plastic wrap, and refrigerate for 30 minutes.

Roll out the dough to about ¼ inch thickness on a floured surface.

Cut out circles with a 3-inch cookie cutter; use a smaller cutter to make heart shapes in half of the circles.

Arrange cookie cutouts on baking sheets and bake for 15-20 minutes or until edges are golden. Let cool.

Dust heart-cutout cookies with icing sugar. Spread strawberry jam on the remaining cookies and sandwich them together.