Cut off about 1 inch from both ends of all 4 oranges; reserve the ends. Stand 1 orange cut-side down on a cutting board. Working from top to bottom, cut away the peel and pith. Cut the orange into 3 rounds, each about 3/4-inch-thick, transferring the rounds to a medium bowl as you work. Repeat with the remaining oranges. Refrigerate the slices until needed.
Squeeze the juice from the reserved orange ends into a small saucepan. Add the orange zest, honey and any remaining juice from your cutting board, and bring to a boil over medium-high heat. Boil, swirling the pot occasionally, until syrupy, about 6 minutes. Toward the end, the surface will be covered with big brownish bubbles. You should have about 1/4 cup of syrup. Let cool to room temperature, about 25 minutes.
Meanwhile, heat a small skillet over medium heat, add the pistachios and cook, tossing frequently until fragrant and toasted, about 4 minutes. Let cool, then chop.
Whisk together the yogurt, half the syrup and the orange-blossom water in a medium bowl.
In each of 4 shallow bowls, layer 3 orange slices with 1 tablespoon of the yogurt mixture, beginning with an orange slice and ending with yogurt. Drizzle the remaining orange syrup over the tops, sprinkle with pistachios and serve.
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