Preheat your oven to 180 C/ 350 F. Line a 8 inch square baking pan with parchment paper or foil, keeping two opposite sides of the parchment long (to help pull out after baking).

If using the strawberry , blend the strawberries with the sugar to get about 1/4 cup of thick puree. Consistency should be as close to a ketchup as possible. Chill this until using.

Chop up the chocolate into very small pieces, cube the butter .

In a bowl placed over a pan of little simmering water (bottom of bowl shouldn't touch the water) - this is called double boiler, melt the chocolate and butter until smooth. You can do the same in a microwave at low power . Stir frequently whichever way you use.

To this melted mixture , stir in the sugar with a whisk.

Add the eggs , one by one, stirring well after each addition.

Stir in the vanilla .

Add the flour and salt , stir in until combined.

Pour batter into the prepared pan.

If using strawberry , add large dollops of the puree all over the top , leaving some space between drops.

Run a knife through the batter in a zig zag manner , connecting the dots to swirl the puree in.

Bake for 25- 28 minutes until a toothpick inserted in centre comes out with a few moist crumbs. The edges will be a light golden brown.

Cool in pan completely and then slice!