Preheat your oven to 180 degrees and line a 12 hole muffin tray with paper cases.
In a large mixing bowl, sift together the plain flour, cocoa, bicarbonate of soda and baking powder. Stir through the caster sugar and make a well in the centre.
In a large jug, add the buttermilk, vegetable oil, eggs, red food colouring and vinegar - stirring with a small whisk or fork until combined.
Pour the liquid into the well, and use a large metal spoon to combine the mixture - be careful not to over mix.
Spoon the mixture into the prepared paper cases and place in the oven to bake for 20 minutes, or until the muffins have cooked through.
Remove the cooked muffins from the oven and allow to cool in the tin for five minutes before carefully transferring to a wire rack to cool completely.
While the cupcakes are cooling you can make the cream cheese frosting.
Place the softened cream cheese, butter and vanilla extract in a large bowl before sifting the icing sugar over the top. Using electric beaters, start mixing the ingredients together on a low speed before increasing to a medium/high speed. Continue to mix until all the ingredients have combined.
Place the TimTams onto a cutting board and chop into large pieces.
Spread the cream cheese icing over the top of the cupcakes using either a spatula or a piping bag before decorating with the TimTam pieces.