When read to make the gelatin, bring the mil to a boil in a medium saucepan over medium-high heat, then immediately remove from the heat and add the baking soda, sugar, and cinnamon bark.
Soak the gelatin in 1/3 cup of cold water. Add to the milk mixture with the rompope, stirring until the gelatin is completely dissolved.
Whip the cream in a bowl until it stands in peaks. Fold the whipped cream into the gelatin and pour into a light oiled 1-quart mold or 4 individual molds. Chill for at least 3 hours before unmolding. This can be made up to 1 day in advance.
Turn the mold out onto a chilled serving plate and cut into wedges to serve, or put the 4 molds on individual dessert plates. Spoon a few berries on the top and around the side of the gelatin.