To make the vinaigrette the first thing we need to do is cut the orange and grapefruit into segments. With a sharp knife, trim both ends of each piece of fruit. Set a flat side of the orange on the cutting board. Remove the peel by cutting around the orange, following the shape of the sphere. Discard the peels and now you’re ready to slice segments: Set the fruit on its side in a shallow bowl. Cut toward the center, along a membrane. Then slice along the adjacent membrane until the cuts meet, releasing the segment. Transfer the segment to a bowl. Repeat until all segments are in the bowl. Squeeze the juice out of the remaining orange membranes, picking out any seeds as you go. Reserve juice and fruit for serving. Repeat this for the grapefruit. By the end, you will have a bowl of orange and grapefruit segments and juice. Add the shallot, extra virgin olive oil, a pinch of salt, black pepper, and red chile flakes to taste. Reserve.