Double-layer chocolate and peanut brownies

Preheat the oven to 180 ºC and butter a 23 cm square cake tin. Dust lightly with flour and shake out the excess.
Melt the chocolate in a glass bowl over hot water for in the microwave oven), stirring until smooth. Remove from the heat and cool to room temperature.
Beat the butter and sugar in a large mixing bowl until light and creamy. Beat in the eggs one by one, beating well after each addition. Stir in the vanilla essence.
Sift the flour, baking powder and salt over the mixture and stir until just blended.
Divide the mixture between two equally large mixing bowls. Add the melted chocolate and half the chocolate chips to the one part and the peanut butter and remaining chocolate chips to other. Stir until just blended.
Turn the peanut butter mixture into the prepared baking sheet and spoon the chocolate mixture on top, spreading evenly.
Bake for 30-35 minutes or until a testing skewer comes out with crumbs adhering to it. Cool completely in the pan and cut into squares with a sharp knife.
Makes 16 fairly large squares.