Whisk together salt, flour and cornstarch. Set aside.
Cream together butter and icing sugar until well combined and pale yellow in colour.
Add vanilla and thoroughly combine.
Stir in dry ingredients and continue to mix until the dough comes together.
On a long piece of plastic wrap (approx 16 inches), place sprinkles in the centre, 10 x 3 inches long.
On a clean counter surface or in your hands, form the cookie dough into a cylinder. Please dough on sprinkles and roll into an even-shaped cylinder; it should be covered in sprinkles.
Keep the cookie dough wrapped in plastic wrap and refrigerate for 30 minutes, or ideally overnight.
Slice dough into 3 cm (½ inch cookies)
Bake on a parchment-lined baking sheet in a 325°F oven for 12 minutes.