Preheat the oven to 190°C/170°C fan and line an 8inch/20cm square tin with greaseproof baking paper or non-stick foil.
Break up the chocolate into a microwave safe bowl.
Melt the chocolate in the microwave in 30 second intervals, stirring in between until the chocolate has melted.
Stir in the oil and set aside.
In a large bowl, combine the sugar, protein powder, flour and bicarbonate of soda.
In a separate bowl, mix together the yoghurt, egg, egg yolk, maple syrup and vanilla extract.
Add the wet ingredients, including the melted chocolate and oil mixture, to the dry ingredients and fold together.
Add the mixture to your prepared tin, making sure it goes right up to the edges and is level.
Scatter the chocolate chips over the top and bake for 16 – 18 mins. The brownie should have a slight wobble and the top should be firm to the touch.
Leave the brownie to cool in the tin.
Slice into 9 large or 12 small portions and enjoy!
