Cut off the peel of the grapefruit and oranges: slice off the ends, then angle your knife and follow the curve to remove the peels (follow Steps 1 & 2 of How to Cut an Orange). Slice the citrus into rings.
Thinly slice the shallot into thin rings.
In a medium bowl, stir together the white wine vinegar, Dijon mustard, maple syrup, and 1 pinch kosher salt. Then gradually whisk in the olive oil 1 tablespoon at a time until creamy.
Arrange the citrus and shallots on a platter or serving plates. Drizzle with vinaigrette. Top with torn mint leaves and fresh ground pepper. If desired, top with finely crushed pistachios.