Preheat oven to 180° celsius
Line muffin tins with cupcake papers
Sift the flour and bi carb soda and set aside
In the bowl of a stand mixer, beat butter until smooth
Add both sugars and beat until fluffy. This should take a few minutes
Add the eggs, one at a time and beat well
Mix in the chocolate
In a small jug, combine the buttermilk and vanilla
To the mixing bowl, add the sifted flour and bi carb in 3 parts, alternating with the buttermilk and vanilla.
Scrape sides and bottom of bowl, then mix until batter is smooth
Fill the cupcake papers about ⅔ full (I use an ice cream scoop)
Bake for 20 minutes. Test with a cake tester -it should come out clean
Allow cupcakes to cool in pans for 15 minutes, before cooling completely on a cooling rack