Preheat oven to 180°C.

Grease a 20 cm square cake tin and line the base with baking paper.

Combine butter and baking chocolate in a pot.

Stir over low heat (or in a double boiler) until melted and smooth.

Cool slightly.

Stir in caster sugar and eggs into the chocolate mixture.

Add sifted flour and mix well.

Fold in chocolate chips (Jaffas).

Spread the mixture evenly into the prepared tin.

Bake for about 35 minutes, or until firm to the touch.

Let stand for 15 minutes before turning out of the tin.

Cut into squares and serve.