Line a 20x20cm tin and preheat the oven to 170ºC (fan assisted or 190ºC non fan)
Cream 300g margarine and 265g caster sugar together until light and fluffy - approx 5 mins
Add 4 eggs and 2 tsp vanilla extract and mix to combine
Add 330g plain flour, 2 tsp baking powder, a pinch of salt and 160g low fat yogurt
Pour half of the cake mix into the prepared tin and smooth out
Using 100g raspberry jam, add dollops on top of the cake and then run a knife or skewer through the jam to create a swirl pattern
Add the rest of the cake mix before smoothing out and repeating the same process as before with another 100g raspberry jam
Bake for 50-55 minutes until a cocktail stick comes out clean
Leave to cool slightly in the tin before allowing to cool completely on a wire rack. Once cooled cut into 16 equal squares
