In a china or glass bowl, stir together the lemon juice, liqueur and honey or sugar, adding the bitters, if using.
Cut the pineapple into 2.5 cm (1 in) cubes and add them to the marinade, then add the strawberries. Stir well, taking care not to break up the fruit, then cover and refrigerate for at least 1 hour, or overnight.
Lift the strawberries and pineapple from the marinade, reserving the liquid, and thread them alternately onto eight skewers.
Dust the fruit with 1 tablespoon of icing sugar, then place the skewers on the barbecue, sugared side down, and cook for 4-5 minutes. Remove from the barbecue, dust the other side of the fruit with the remaining sugar and barbecue again, sugared side down.
Divide the skewers between four plates and drizzle the marinade over. To decorate, sift a little icing sugar over each, then serve.
Variation: try other combinations of fruit, such as pears, strawberries and kiwi fruits, or fresh dates and figs.