Begin by preparing your molds and cream base. Brush 4 × 5fl oz (150ml) ramekins or metal molds with sunflower oil and arrange them on a pan. In a small bowl, measure 3 tablespoons of cold water, sprinkle 2 teaspoons of powdered gelatin over the top, and let it sit until spongy.
While the gelatin hydrates, pour 2½ cups of whipping cream into a saucepan and add ¼ cup of granulated sugar. Finely grate the zest from the oranges and add it to the pan along with 2 tablespoons of orange liqueur.
Heat the cream mixture until bubbles form around the edges, stirring constantly until the sugar dissolves completely and the cream is smooth. Remove from heat and allow it to cool slightly before proceeding to the next step.
Once the cream has cooled, add the sponged gelatin to the warm cream and whisk vigorously until it is completely dissolved and the mixture is smooth. Carefully pour the cream mixture into the prepared, oil-brushed molds.
Transfer the pan to the refrigerator and chill for approximately 6 hours, though ideally overnight, until the panna cotta is fully set and has achieved its characteristic wobble.
While the panna cotta sets, prepare the soaked oranges for serving. Using a serrated knife, peel and segment the remaining oranges, working over a bowl to capture all the juice. Place the orange segments into the bowl and squeeze the thick, white membranes over it to extract every drop of remaining juice.
Stir in the remaining ¼ cup of orange liqueur and refrigerate the mixture until serving time. To serve, briefly dip each mold into very hot water, gently loosen the panna cotta from the top with your fingertips, and carefully invert it onto a plate. Present each chilled panna cotta with a spoonful of the soaked oranges alongside.
