75g unsalted butter, chopped
250g dark cooking chocolate, finely chopped
½ cup caster sugar
1/3 cup cocoa powder
1 teaspoon vanilla extract
1 cup plain flour
1 teaspoon baking powder
150g dark cooking chocolate, chopped
¼ cup thickened cream
Grease and line three large oven trays with baking paper.
Combine butter and 150g of the finely chopped chocolate in a large heatproof bowl. Sit bowl over a saucepan of simmering water. Stir until melted and smooth. Remove bowl from heat. Stir in sugar and sifted cocoa until combined. Stand for 15 minutes.
Whisk together eggs and vanilla in a small jug. Stir into chocolate mixture. Fold in combined sifted flour and baking powder. Fold in remaining finely chopped chocolate. Refrigerate, covered for 20 minutes, or until firm.
Roll tablespoons of mixture into balls. Place, 5cm apart, on prepared trays. (About eight on each tray). Using the palm of your hand, flatten slightly.
Cook two trays, in a moderately slow oven (160C), swapping halfway, for about 15 minutes, or until just firm to touch. Remove. Cool on trays completely. Repeat with remaining tray.
To make ganache, combine chocolate and cream in a heatproof bowl. Sit bowl over a saucepan of simmering water. Stir until melted and smooth. Remove bowl from pan. Refrigerate, stirring every 10 minutes, for about 40 minutes, or until thick.
Spoon 2 teaspoons of ganache onto the base of half the cookies. Sandwich with remaining cookies.