Begin by creaming together your butter and sugar for about 2 minutes until light and airy.
Next add in your egg and vanilla, beating to combine.
Sift the flour, salt and baking powder into the mixing bowl with the sugar mixture and use a spatula to begin stirring together. Then add the milk and stir to combine into a thick dough.
Form the dough into a ball and wrap in plastic wrap or cling film. Flatten slightly into a disk and refrigerate for about an hour.
Meanwhile, preheat your oven to 375°F (190C/170C Fan) and line a couple of baking sheets with parchment paper or silicone baking mats.
When the dough has chilled, remove from the refrigerator, unwrap and place on a lightly floured work surface. Using a rolling pin, roll the dough out to about ⅛" thickness. Use cookie cutters to cut out designs and place these on your prepared baking sheets.
Reroll the cookie dough as many times as necessary to use this up. The dough is enough for about 18-20 cookies using small and medium cookie cutters.
Bake the cookies in your preheated oven for about 8 minutes. Exact times will vary based on size and thickness of the cookies, but look for edges to start going ever so slightly golden.