The classic flavor combination of fennel and orange makes a wonderful winter salad.
In a large bowl, whisk together vinegar and oil; season with salt and pepper.
Using a sharp knife, slice off both ends of each orange. Following the curve of the fruit, cut away the peel and white pith. Halve orange from top to bottom; thinly slice crosswise. Transfer oranges, along with any juices that have accumulated on work surface, to bowl with dressing. Add fennel and, if desired, fronds. Toss to combine.
