I reduced the sugar from 2 cups to 1 cup only because I found 2 cups was too sweet.
I used melted 50-70 grams (i think) of 56% cooking chocolate which was left over from my previous baking session. I chopped the chocolate into smaller pieces and used double-boil method to melt it.
It's important to mix the batter once they're in the pan to create the marble pattern. Just use a knife or chopstick with slow swirling motion along the pan. I didn't do this on my last baking so I didn't get the marble pattern :(
3/4 cup unsalted butter, softened at room temperature
1/4 cup vegetable oil
1 cup granulated sugar
1 cup whole milk
1 tbsp vanilla extract
2 tsp baking powder
2 1/2 cups all purpose/plain flour
1/2 cup cacao powder or double-boil melted cooking chocolate
1/2 tsp salt
1. Preheat the oven 325 deg Fahrenheit (around 163 deg Celcius), spray pan with non-stick spray or use butter + flour
2. In a small bowl, mix together the flour, baking powder, vanilla, salt. Set aside.
3. In large bowl, whisk together the oil, butter & sugar until creamy. Add the eggs & continue to mix until thick & pale.
4. Add milk & mix quickly, add flour mixture & mix all together but don't over mix.
5. Pour 2/3 of the batter to the pan
6. Add cocoa powder or mix the melted chocolate to the remaining batter & mix well.
7. Pour the chocolate batter to the pan. Use a knife or a chopstick in swirl motion to create the marble pattern.
8. Bake for around 1hour 15 minutes. Let it cool completely before serving.