Preheat your oven to 350°F/180°C. Line an 8x8-inch baking tray with parchment paper.

In a large mixing bowl, beat the softened butter and sugar until light and fluffy. This should take about 2-3 minutes.

Mix in the vanilla extract, orange extract(optional), and a pinch of salt until well combined.

Sift in All-purpose flour. Mix just until the dough comes together.

Transfer 1/3rd of the dough into another bowl. Into the 2/3rd portion add chocolate chips. Combine with a spatula.

Into the 1/3rd portion add cocoa powder. Combine well.

Take out small chunks from both chocolate and vanilla dough. Randomly place them in the prepared baking tray to create a marble effect.

Using your hands or flat-bottomed utensil flatten the dough into a smooth even layer.

Score/cut the dough with a sharp knife/scrapper into approximately 1-by-4-inch bars(or your preferred shape). Use a fork to prick the surface of the cookie dough.

Bake at 180℃/350℉ for 35 to 40 minutes. Let stand for 5 minutes in the pan, then re-cut the bars along the previous cuts. Carefully lift the bar off the baking tray with the help of the overhang parchment paper. Transfer each bar to a wire rack to cool completely.