Preheat the oven
to 325°F/170°C/gas 3. Butter two cookie sheets.
Sift the flour,
cocoa, baking powder, and salt into a large bowl.
Beat the butter and sugar in a large bowl with an
electric mixer at high speed until creamy.
Add the egg,
beating until just blended. Mix in the dry
ingredients, followed by the peanuts.
Drop teaspoons of
the dough 1 inch (2.5 cm) apart onto the prepared
cookie sheet.
Bake for 20-25
minutes, or until crisp and golden brown. Cool on
the sheets until the cookies firm slightly. Transfer
to racks to cool.