Instructions

1. Chocolate whoopie pies
   In a large mixing bowl, beat butter and sugars with an electric mixer on medium speed until pale and creamy. Add egg and vanilla and beat until combined.
2. Sift in the baking soda, plain flour and cocoa powder. Add half the buttermilk and beat briefly, before adding the rest of the buttermilk. Beat until the mixture is combined and smooth, it will be quite wet – similar to cake batter.
3. Cover the batter with plastic wrap and pop into the freezer for at least 30 minutes. This will help firm up the mixture.
4. Preheat oven to 180 C (350 F) standard / 160 C (320 F) fan-forced. Line two oven trays with baking paper. Use a cookie scoop to spoon out cookies (approximately 1.5 tablespoons each) onto prepared trays, leaving space for them to spread out when cooking.
5. Bake for approximately 10 minutes. Leave them to cool for a few minutes and then transfer the cookies onto a wire rack to cool completely.
6. Marshmallow filling
   Fill a medium saucepan with a few inches of water and pop on a medium heat. In a heatproof bowl, add eggs whites, sugar and cream of tartar. Whisk together.
7.  Pop the bowl over the top of the saucepan, ensuring the bottom of the bowl does not touch the water below. Whisk gently as you slowly heat the egg whites.
8. Use a candy thermometer, to heat the egg whites to 65 C (150 F) – should be around 5-6 minutes or so.
9. Remove bowl from the saucepan and transfer mixture in a large mixing bowl and beat using an electric mixer on medium speed for approximately 5 minutes or until the mixture becomes fluffy, white and glossy. Add vanilla and beat for an additional 30 seconds or so.
10. Transfer marshmallow fluff to a piping bag inserted with a large round tip or use small spatula to spread marshmallow filling onto a whoopie pie and sandwich together with another whoopie pie. Repeat with remaining cookies and marshmallow fluff.