In a food processor, blend the ricotta cheese until light and fluffy about 10 seconds. Add the jam, ½ of the strawberries and the zest of an orange and pulse until combined. Transfer to a large bowl. In a separate bowl, use an electric hand mixer to beat the cream until it holds stiff peaks. Working in batches, carefully fold the cream mixture into the ricotta mixture until you obtain a light mousse. Next, make the soaking syrup.Put the strawberry liqueur in a small saucepan along with the caster sugar and boil for 2 minutes. Remove off the heat, squeeze the juice from the oranges and add to the liqueur. Allow to cool completely. Dip the sponge fingers into soaking syrup and lay side by side into a serving dish. Cover with half of the strawberry mousse and repeat the process again, using the remaining sponge fingers and strawberry mousse. Decorate the top with the remaining 100g of fresh strawberries and refrigerate for 1 hour. Garnish with fresh mint leaves before serving.