Line two baking trays with non stick baking parchment.
Melt the butter over a low heat, then leave to cool until lukewarm.
Meanwhile, whisk the egg whites until stiff but not too dry and gradually whisk in the sugar.
Using a metal spoon, fold in half the flour, then pour the butter around the edge of the mixture in the bowl.
Gradually add and fold in the remaining flour, at the same time working in the butter.
Lastly fold in the orange rind.
Drop teaspoonfuls of the mixture well apart on the prepared baking trays and spread out to give thin, even rounds about 10 cm/4 in. in diameter.
Bake in a moderately hot oven (190C, 375F, gas 5) for 7-8 minutes or until golden brown round the edges.
Allow the biscuits to cool on the trays for a few seconds so that the mixture will stay together when lifted.
Using a large palette knife, carefully remove the biscuits from the trays while they are still hot. (If the mixture hardens on the trays replace them in the oven for about half a minute, or until the biscuits soften.)
Quickly wrap each biscuit around a cream horn tin and place on a wire rack until cool.
Continue cooking the biscuits in this way until the mixture is used, re lining the trays if necessary.
To finish the trumpets, whip the cream with the orange liqueur until stiff.
Spoon the cream into a piping bag fitted with a star nozzle and pipe it into the trumpet shells.
Decorate each one with a whole strawberry and serve within an hour of filling, or the biscuits will loose their crisp texture.