Preheat the oven to 180 C / Gas 4. Grease a shallow cake tray and line with baking parchment.
Mix together margarine, sugar and vanilla until light and fluffy. Add eggs one at a time, beating after each addition. Stir in the remaining ingredients and mix well. Pour into prepared tray, smoothing the top.
Bake in the preheated oven for 35 to 40 minutes, or until a skewer poked in the centre comes out clean. Cool 5 minutes in tray, then remove to wire rack. Cover and cool completely before serving.