For the cake:
100-gram soft margarine
100-gram caster sugar
2 large eggs beaten
100-gram self-raising flour
1 teaspoon baking powder
For the topping:
200-gram strawberries
200-gram blueberries
1 tablespoon of sugar
2 tablespoons of water
Metric - US Customary units

For the cake
Heat the oven to 350F/180C/Gas 4 and grease and line a 7-inch cake tin. I used a deep cake tin to get one sponge but you could split the cake between two tins if preferred.
Place all the ingredients in a bowl and beat well until blended and smooth.  Spoon into the tin and smooth the top. 
Bake for 25-30 minutes if using two tins and 35-40 minutes for the deeper tin, test with a skewer which should come out clean when the cake is baked.
Turn the cake onto a cooling tray and leave to cool
For the topping
Hull the strawberries, slice up 6-8 strawberries (depending on size) and heat gently in a pan with a tablespoon of sugar and 2 tablespoons of water. 
Simmer gently until the sugar has dissolved and the berries start to soften, crush the berries and cook for a further 2 minutes until jammy. You should still have some juice left, leave to cool.
Cover the top of the cake with the 'jam', reserving a couple of teaspoons of the juice.  Arrange halved strawberries around the edge of the cake and fill the middle with blueberries, brush the berries with the reserved juice to add shine.

Serve with cream, ice cream, or yogurt.
Calories: 303kcal | Carbohydrates: 38g | Protein: 4g | Fat: 15g | Saturated Fat: 3g | Cholesterol: 54mg | Sodium: 180mg | Potassium: 187mg | Fiber: 1g | Sugar: 23g | Vitamin A: 695IU | Vitamin C: 22.9mg | Calcium: 52mg | Iron: 0.7mg