In a large mixing bowl, combine the flour, butter (cubed or cut into chunks), sweetener, and any other flavorings you are using.Mix and knead the dough together, using your hands, and make sure the butter is fully incorporated.Chill the dough for at least 1 hour in the fridge.Preheat the oven to 325°F.Line an 8x8 or 9x9 inch square baking pan with parchment paper.Remove the dough a few minutes before you try pressing it into the pan or rolling it out for the cut-out method.Press the dough into the lined pan, about ½ inch thickness, and smooth out the top.Take a sharpe knife to score your bars or squares and prick the centers with a fork.Bake the shortbread in the preheated oven for 35-40 minutes.Remove the shortbread and while still warm, fully slice through the scored sections.Lift the cookies out of the pan, using the parchment paper and then transfer each cookie carefully to a wire rack to cool completely.