Preheat oven to 425°F (220°C).

Lightly grease a baking sheet.

In a large mixing bowl, combine flour, baking powder, baking soda, salt, and sugar.

In a separate bowl, blend together peanut butter and egg white. Add milk and whisk well.

Stir the peanut butter mixture into the flour mixture.

Combine the butter mixture with the flour using a fork.

Knead with your hands until a workable dough forms.

Pour dough onto the prepared baking sheet.

Flatten the dough lightly with your hands or fingers.

Cut into 8 wedges.

Brush with milk.

Sprinkle with extra sugar.

Bake in the preheated oven for 12-15 minutes, or until golden brown.

Cool on a wire rack.