Cream the butter and sugar: In a bowl, cream the room-temperature butter and sugar until light and fluffy. Add the molasses and beat until combined. Then, add the vanilla extract and egg, mixing well until fully incorporated.
Add the dry ingredients: Stir in the flour, spices, and salt. Mix with a spatula or on low speed until just combined; do not overmix.
Chill the dough: Wrap the dough in plastic wrap and refrigerate for at least 1 hour (or overnight) until firm. This will make the dough easier to handle.
Roll out and bake: On a lightly floured surface, roll out the dough to about 1/2 cm (1/4 inch) thick.
Cut out shapes using cookie cutters and place them on a baking sheet lined with parchment paper or a silicone baking mat.
Bake in a preheated oven at 180°C (350°F) for about 8 minutes, watching carefully so they don't brown too much. Remove them from the oven and let them cool on the baking sheet for a few minutes before transferring them, as they will be fragile while hot.
In a bowl, beat the pasteurized egg white with the powdered sugar for about 5 to 7 minutes, until you obtain a glossy white icing.
Place the icing in a piping bag and decorate the cookies once they have cooled completely.
Let the icing dry at room temperature until it hardens. You can decorate with sprinkles or anything else you like.