Sugar cookies are a holiday classic; these festive sandwiches can be filled with any variety of jam or jelly, or even Nutella.
In a large bowl, beat the butter and sugar for 2-3 minutes, until pale and light.
Beat in the egg and vanilla.
Add the flour and salt and beat on low speed or stir by hand just until you have a soft dough.
Divide the dough in half, shape each into a disc, wrap in plastic and let rest or refrigerate for at least an hour, or for up to a few days.
When you’re ready to bake, preheat the oven to 325˚F.
On a lightly floured surface, roll each piece of dough out to about 1/4-inch thick. Cut into 2 1/2—inch stars, hearts, rounds or other shapes with a cookie cutter or glass rim, and cut smaller windows out of half of the cookies with a smaller cutter.
Transfer to a parchment-lined sheet and bake for 10 minutes, or until pale golden around the edges and set. Transfer to a wire rack to cool.
Spread the solid cookies with jelly or jam.
Place the cookies with windows on a baking sheet and sprinkle with icing sugar, then place them on top of the cookies spread with jam.