Preheat oven to 180°C (160°C for fan assisted ovens)/Gas Mark 4. Grease a 2 litre ovenproof bowl (about 20cm across the top) with a little softened butter, then dust with flour. Lightly grease 3 muffin holes in a regular size muffin tin with butter.
Mix the cake mix, oil, water and eggs gently together in a medium bowl and whisk (by hand or electric mixer) for 2-3 minutes, until smooth and creamy.
Spoon some of the cake mixture into the 3 greased muffin holes, filling to 2/3 full. Pour the remaining cake mixture into the ovenproof bowl.
Place in the oven and bake the cupcakes for 18-22 minutes and the bowl for 55-65 minutes or until a skewer inserted into the centre comes out clean. Leave to cool for 10 minutes on a wire rack then remove the cakes from the muffin tin and bowl. Place rounded sides up on wire rack and leave to cool completely, (about 1 hour for the large cake). Cut off the rounded tops from the cake and 2 of the muffins.
Spoon nearly all the icing into a large bowl (reserve 2 tablespoons for the carrots) and beat in enough pink food colouring paste or gel to make a pale pink colour. Place the bowl cake on the cake board, cut side down and spread 1/2 of the icing over the cake using a small palette knife. Use the icing to adhere the cupcakes to the bowl cake for the feet and bunny tail. Use toothpicks to secure in place, if necessary. Place a marshmallow half, cut side down, on top of each cupcake 'foot' to resemble heels. Spread a thin layer of icing over and around the cupcakes. Chill the cake for 30-45 minutes to set the icing.
Spread nearly all the remaining icing over the cake (reserve a little to spread on the cake board). Roll out the fondant icing on a surface lightly dusted with icing sugar. Use a rolling pin to roll out into a small circle about 3-4mm in thickness. Stamp 2 circles out with the larger cutter and 6 small circles out with the smaller cutter. Press the large circles into ovals and stick onto the bunny feet with the smaller rounds.
Sprinkle the whole cake liberally with 2/3 of the coconut and press gently into the icing to make sure it stays in place. Shake the remaining coconut together with a little green food colouring paste or gel in a resealable food bag, until evenly tinted. Spread the remaining pink icing on the cake board and cover with the green coconut, pressing it down gently.
Scatter the cookie crumbs in patches on the coconut 'grass' to resemble mud. Beat the reserved white icing with a little orange food colouring paste or gel in a small bowl until evenly coloured. Spoon into a piping bag fitted with a plain nozzle. Pipe a few 'carrots' in the cookie mud. Just before serving the cake add the mint sprigs to resemble carrot tops.
Cut ears from the card and wrap the ends that will be inserted into cake with cling film. Insert into the cake. Remove the ears, cling film and toothpicks before serving. Store the cake loosely covered with cling film in a cool place for 2-3 days.