Place the flour , sugar , cocoa powder and 145grams of the butter together into a bowl or food processor and combine until mixture resembles fine bread crumbs .

Make a well in the middle of the dry ingredients and add the whisked egg and the milk and combine until dough comes together , then turn onto a lightly floured surface and knead dough until smooth . Now divide the dough in half , shape halves into 2 discs , wrap in plastic wrap and refrigerate for 30 minutes , till chilled and firm .

Take the chilled dough discs and roll one disc between two sheets me baking paper until about 5mm thick , now using a 4cm - square cookie cutter , cut out squares from the dough (note if dough becomes too soft , refrigerate until firm) , repeat with second dough disc to make a total of 50 dough squares .

Once chilled , place baking trays of biscuits into the oven and bake , 1 tray at a time , for 8-10 minutes . Once cooked remove from heat and stand on trays for 5 minutes then transfer to a wire rack to cool completely .

TO MAKE CHOCOLATE CREAM : place 50 grams of the dark chocolate into a heat proof bowl and microwave on high for 45 second bursts , stirring and each burst , until melted and smooth , cool for 5 minutes . In a separate bowl add the butter and icing sugar and beat till light and fluffy , then add the vanilla and the melted chocolate and stir to just combined (don't overbeat) .

Spread about 1 teaspoon of the cream filling mixture onto one of the little prepared square biscuits and top with another biscuit so to sandwich together . Repeat with all and refrigerate for about 20 minutes to chill through .

Place the broken up milk chocolate and the remaining broken up dark chocolate into a heatproof bowl and microwave on high 45 second bursts , stirring at each burst) until melted and smooth .

Set a wire cooling rack over some baking paper , now dip each side of the square filled sandwiches into the chocolate to cover all the sides , place on rack to set , repeat with all . Now place a spoonful of the melted chocolate into the tops of each side chocolate coated biscuit sandwich and leave on wire rack to set completely .

Once set turn chocolate coated biscuits over and repeat with chocolate to cover the bottoms , leave to set completely . Refrigerate for best results .

Once set , place on plate , serve and enjoy . :-) .