Preheat the oven to 350 degrees F.

Place the butter and bittersweet chocolate together in a large heavy based pan over a low heat.

In a bowl, beat the eggs together with the sugar and vanilla extract.

Add the egg and sugar mixture to the chocolate and beat well.

Add the flour and salt. Then stir in the chocolate chips. Beat to combine then scrape and pour half of the mixture into the prepared baking pan.

Spread the dulce de leche over the mixture. Pour the remaining brownie batter over the dulce de leche layer.

Bake for about 25 to 30 minutes.