►CITRUS VINIAGRETTE: Trim the tops and bottoms off grapefruits and stand them up on the cut (flat) surface. Working in sections, slice lengthwise between flesh and peel, following fruit’s contour and making sure all pith and peel are removed.
►Working over a bowl to catch juice, slice lengthwise between one segment and the membrane until you reach the center. Repeat with other side of segment and remove segment with knife. Transfer to a medium bowl. Repeat process until all segments are removed. Squeeze juice from remaining membrane into working bowl, then discard membrane. Strain juice and transfer to a small mixing bowl or mason jar—you should have about ¼ cup juice.
►To the bowl or jar, add shallots and let sit for 10 to 15 minutes. Add honey, mustard, and lemon juice and whisk (or cover with a lid and shake) to combine. Pour in oil and whisk to combine until vinaigrette has emulsified. Taste and season with additional salt and pepper as necessary. Set aside.
►TO ASSEMBLE: Lay out arugula on a large serving platter and top with radish, fennel, and grapefruit segments. Top with marcona almonds and Fiore Sardo PDO cheese. Season with flaky sea salt and black pepper and serve with vinaigrette on the side.