Cook the shrimp: Fill a large bowl with water and add plenty of ice; set aside. Fill a large pot halfway with water. Add 1/4 cup dill, 2 smashed garlic cloves, a nice pinch of salt and a few grinds of pepper. Bring to a boil, then reduce the heat to medium low and simmer until fragrant, about 5 minutes. Add the shrimp; remove the pot from the heat and let sit, stirring occasionally, until the shrimp is pink and opaque, 2 to 3 minutes. Drain and transfer to the ice bath to cool.
Combine the remaining 1 cup dill, 1 grated garlic clove, the mayonnaise, sour cream, yogurt, cucumber, onion, lemon zest and sugar in a large bowl. Taste, then season with a pinch of salt and a few grinds of pepper.
Remove the shrimp from the ice bath, dry gently with a paper towel and coarsely chop. Stir into the dressing until combined.
Cut the iceberg lettuce into 4 wedges. Tear the first few layers from the center of each wedge to create a "bowl" in the wedge; divide among plates. Fill the lettuce bowls with the shrimp salad, letting it spill over the wedge. Garnish with chopped dill. Serve cold or at room temperature.
Photograph by David Malosh
Courtesy of Food Network Magazine