In a large bowl, mix the flour, baking powder, salt, ginger, cinnamon, allspice, cloves, and nutmeg. Set aside.
In another large bowl, using a handheld mixer or stand mixer fitted with a whisk attachment, beat the butter on medium speed until creamy, about 1-2 minutes. Add brown sugar and molasses and mix until combined. Add egg and vanilla and mix until fully combined. Add dry ingredients and mix on low speed until combined. The dough will be sticky and thick. Knead it by hand a few times and divide in half. Shape into discs and wrap tightly in plastic wrap. Refrigerate for at least 3 hours or up to 3 days.
Preheat the oven to 350°F / 175°C and line 3 baking sheets with parchment paper and set aside.
On a well-floured surface, roll out the dough discs to a thickness of ¼-inch (6mm). Using a 4-inch (10cm) gingerbread man cutter, cut out cookies and place on prepared baking sheets, leaving about 1-inch (2.5cm) between them. Then bake for 8-9 minutes. Cool on baking sheets for 5 minutes, then transfer to a cooling rack to cool completely.
OPTIONAL: Whisk together the sugar, water, and salt until combined. Place in a piping bag and cut off a small piece of the tip. Decorate the cooled cookies as desired. Store in an airtight container at room temperature for up to 1 week.