In a large bowl, whisk together the sugars, salt, and butter until a forms into a paste-like mixture.
Whisk in the egg and vanilla, until no lumps remain.
Sift in the flour and baking soda, then mix using a spatula.
Add the chocolate chip into the batter, then chill the dough for about 20 minutes.
Preheat the oven to 350°F (180°C), Line a baking sheet with parchment paper.
After chilling the dough, put some flour on the table, put the dough on it and mix it with your hands until you're able to shape the cookies.
Shape the dough into a flat disc, cut out animal shapes, and place on a parchment paper-lined baking sheet. Leave about 1 inch of space between each cookie and leave some space from the edges of the pan so that the cookies can spread evenly.
Bake for 15 minutes, or until the edges have started to turn brown. Cool the cookies on a wire rack before decorating it with the chocolate icing.
Icing:Melt the dark chocolate for 30 seconds using a microwave (or any heating device).
Add the warm milk or heavy cream to the melted dark chocolate. If the chocolate starts to harden, microwave it to let it melt.
Add the chocolate icing to a piping bag.
Decorate the cookies as how you like.
Tip: Keep the cookies in an airtight container for a day to make them chewy.