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Note: if you're using a chocolate bar, you need to chop it into pieces
PLACE the paper muffin cups into the muffin tins and PRE-HEAT the oven to 190 degrees celsius or 375 degrees Fahrenheit. COMBINE flour, salt, baking soda, baking powder and cocoa powder in the large bowl.
ADD the eggs and egg yolk to the bowl of your standmixer and mix a few minutes. Gradually ADD the sugar and keep on mixing until its fluffy and pale.
ADD the vanilla extract along with the buttermilk and sunflower oil. When the mixture is smooth again, gradually ADD the flour and cocoa mixture until you've reached a smooth batter.
REMOVE the whisk attachment from your standmixer and ADD the chocolate chips to the batter. COMBINE them carefully with a silicone spatula and divide the batter into the paper muffin cups.
FILL them for about 3/4th and sprinkle the top with a little bit of sugar. BAKE the muffins in the oven for about 15 minutes. Check them with a wooden skewer, when the skewer comes out clean, or with only a little bit of melted chocolate, they're done.
Let them cool off a bit before enjoying these lovely chocolate muffins!