In a mixing bowl, using an electric mixer, beat the butter, peanut butter, brown sugar and sugar until creamy. Beat in the vanilla. Add the egg and beat just until it is mixed in, then beat in the salt, baking powder and soda. By hand, stir in the rye flour and the seeds. Dough should be very easy to handle – neither too dry and definitely not sticky. Hopefully you’ve weighed it with a scale.