1) In a medium bowl, sift together the flour, salt and baking powder. Set aside.
2) In the bowl of a standing mixer fitted with a paddle attachment, combine the butter and sugar and beat on medium speed until light and fluffy. Add the egg and vanilla and beat until combined.
3) Add the flour mixture in two batches, scraping down the bowl after each addition. Beat until the dough just comes together, being careful not to over mix.
4) Turn the dough onto a lightly floured surface. Form the dough into a ball, wrap it in plastic and refrigerate for 30 minutes.
5) Place the ball of dough between two pieces of greaseproof paper and roll out to 0.5cm thick. Keeping the dough on the greaseproof paper, transfer to a baking tray and refrigerate for at least 1 hour.
6) Preheat the oven to 180C/Gas 4.
7) Cut out the biscuits in the desired shapes and place on a baking tray lined with greaseproof paper or an ungreased nonstick baking tray, at least 2.5cm apart.
8) Transfer to the freezer and chill for at least 15 minutes or until they are firm.
9) Bake until biscuits are light golden brown, about 10 minutes.
Cool biscuits completely on the sheets before decorating.
*Cook's Note: Biscuits will still be soft when they come out of the oven and may break or become misshapen if they are moved off the sheets before they cool.