Preheat oven to 350 degrees F/160 degrees C.
Line two nine-inch cake pans.
In a stand mixer (or heat-proof bowl and hand mixer), add sugar, brown sugar, cocoa powder, baking soda and salt.
Carefully pour boiling water/coffee into the cocoa mixture.
Allow to cool for 10 minutes.
Add canola oil, melted butter, eggs, egg yolks, and vanilla and blend until combined.
Mix in flour.
Finish by adding sour cream and full cream milk and blend until combined.
Pour into cake pans.
Bake for 30-35 minutes. (Insert a toothpick, and when it comes out clean, it’s done.) For cupcakes, pour into cupcake pans and bake for 10-12 minutes.
Let the cake cool completely before frosting.