Whisk evaporated milk, sugar, orange zest, and gelatin in a small saucepan until gelatin softens and sugar dissolves. Bring milk mixture to a simmer. Remove from heat and stir in liqueur. Pour a scant 1/2 cup into each of four 6-ounce custard cups. Refrigerate until set, about 2 hours. (Panna cotta can be covered with plastic wrap and refrigerated for up to 5 days.)
To serve, run a thin-bladed knife around inside edge of custard cup. Turn out each panna cotta onto a small dessert plate, garnish with raspberries, and serve.
Recipe and image courtesy of Pam Anderson, author of The Perfect Recipe for Losing Weight & Eating Great (2008).