Treacle can be difficult to weigh accurately, as it tends to stick to the scale pan. Weighing it on top of the sugar overcomes this problem.

Makes 15-20 pieces

225g/8oz softened butter
175g/6oz light muscovado sugar
200g/7oz black treacle
300g/11oz self-raising flour
2 level tsp baking powder
1 level tsp ground mixed spice
1 level tsp ground allspice
4 large eggs
4 tbsp milk
3 finely chopped bulbs of stem ginger from a jar

For the icing
75g/3oz icing sugar
3 tbsp stem ginger syrup from the jar
3 finely chopped bulbs of stem ginger from a jar

1. Pre-heat the oven to 180°C/fan 160°C/ gas mark 4. Grease a 30 x 23cm/12 x 9in tray or roasting tin then line the base with baking parchment.

2. Put all the ingredients for the traybake into a large bowl and beat until well blended. Turn the mixture into the prepared tin, scraping the bowl with a plastic spatula to remove all the mixture. Level the top gently with the back of the spatula.

3. Bake in the pre-heated oven for 35–40 minutes, or until the cake has shrunk from the sides of the tin and springs back when pressed in the centre with your fingertips. Leave to cool in the tin for a few minutes then turn out, peel off the parchment and finish cooling on a wire rack.

4. To make the icing, sift the icing sugar into a bowl, add the ginger syrup and mix until the icing is smooth and has a spreading consistency. Pour the icing over the cake, spread it gently to the edges with a small palette knife and sprinkle with the chopped stem ginger to decorate. Allow the icing to set before slicing the traybake into 15–20 pieces.

Recipe taken from Mary Berry's Baking Bible by Mary Berry (BBC Books). To order your copy from the RT bookshop for just £17.99 (usually £25) with free postage and packaging, call 01603 648176.

The Mary Berry Story concludes tonight, 8pm BBC2