Preheat oven to 180°C (355°F) and line a baking sheet with baking paper.
Stir the flour, baking powder, and vanilla together in a large bowl. Add the butter and knead with your hands until crumbly.
Add the sugar and egg and mix with hands until you get a solid ball of dough.
Roll the dough into two long sausages and cut about 30 slices. Roll each slice into a ball. Set the cookies on the baking sheet spaced slightly apart.
Use a fork to lightly press down each cookie. Whisk the egg into an egg wash and brush gently over each cookie. Sprinkle sliced almonds and/or granulated sugar on top of each cookie.