Allow butter to reach room temperature. Cream it in a stand mixer with the sugar and salt, until smooth.

Mix in the flour, until crumbly.

Add the egg and continue to mix, until combined.

Remove the dough from the bowl and press it together into a ball. Wrap it in plastic wrap and refrigerate for at least 30 minutes.

Remove from fridge. Roll the dough into one-inch balls. Flatten the ball into a disc as you roll it in sugar. Place on a Silpat-lined baking sheet and bake in a 375-degree oven for 20-25 minutes, until slightly golden brown.