Preheat your oven to 325°F.

Blend the unsalted butter, icing sugar, salt, and vanilla extract together until fluffy, about 3 minutes.

Gently add the sifted all-purpose flour and mix just until a dough begins to form.

Remove the dough from the mixer and knead it by hand into a smooth ball, about 1 minute.

Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.

On a floured surface, roll out the dough to about ¼ inch thickness.

Use a 3-inch round cookie cutter to cut out cookies, then switch to a 1½-inch heart-shaped cutter to cut centers from half of them.

Place the cookies on a parchment-lined baking sheet.

Bake for 15–20 minutes, rotating the pans halfway through.

Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack.

Once completely cool, dust icing sugar over the cutout cookies.

Spread a generous layer of strawberry jam on the flat side of the whole cookies, then sandwich them with the cutout cookies.