Preheat the oven to 180°C, 350°F, Gas Mark 4. Lightly oil a baking sheet and set aside.
Place the flours, salt, sugar, butter and mint in the bowl, fit dough hook and knead on speed min for 1 minute. Increase to speed 2 for 1-2 minutes, scraping occasionally, until well combined.
Turn out onto a lightly floured surface, knead lightly and roll out to 2.5cm (1/4 in) thick. Using a 6cm (2 1/2 in) round fluted cutter cut out 12 rounds. Place on the baking sheet well spaced apart and bake for 15-20 minutes, until golden.
Transfer to a wire rack and allow to cool completely. Meanwhile place the fruits, icing sugar and Cointreau® in a small pan and heat gently until juices begin to run. Remove from the heat and allow to cool completely.
Place the cream in the bowl, fit the whisk and whisk on speed 3 for approx 2 minutes, until soft peaking. Sandwich the biscuits together with the cream and serve with summer fruits. Decorate with mint leaves and dust with icing sugar.