Prepare cupcake tin for 12 cupcakes with cupcake papers cups and preheat the oven to 160 °C/ 325 F.
In a large bowl, combine all dry ingredients (except brown sugar). Sift the flour & cocoa powder first, then add baking powder, salt and set aside.
Melt the chocolate in the microwave. In medium microwave proof bowl, power 70% for 1 minute. Remove from the microwave, stir and set aside.
In a large bowl of stand electric mixer, cream softened butter and brown sugar together on high until light and fluffy. (About 3-5 minutes).
Add these following ingredients: two extra large eggs, vanilla extract, vegetable oil and melted chocolate. Let each ingredient to get well combined after each addition.
At the end add the dry ingredients reserved earlier. And mix them together with wet ingredients.
Divide the mixture equally into the cupcake tin; use ice cream scoop and add 1 and 1/2 scoop into each tin. Place the cupcake tin in a preheated oven and bake for 20-25 minutes. At the end insert a skewer, if it comes out clean, the cupcakes are done.
Allow cupcakes to stand in the tin on a cooling rack for 10 minutes, then carefully remove and allow cooling completely.