Cut fennel bulbs in half from root to end and slice paper-thin on a mandoline into U-shaped slices.

In a small bowl, combine vinegar, salt, and pepper. Drizzle in olive oil slowly while whisking constantly, or add in the oil and blend the dressing with a handheld milk frother.

Toss fennel and arugula in a large bowl with the dressing.

Cut blood oranges in half and cut off the peel and pith with a knife. Slice each orange half into three rings.

If serving as a main course, slice sausage links lengthwise into two halves and cook over medium high in a pan or indoor grill until charred on both sides.

Divide salad mixture between plates. Top with blood oranges and three sausage halves.