Over low heat, melt butter in a large skillet. Add diced onion with a pinch of salt and sweat slowly until soft.
Stir in sliced garlic and sungold tomatoes. Cook over low-medium heat for 20-30 minutes until the tomatoes burst and release their juices, stirring occasionally.
Bring a large pot of salted water to a boil and cook orecchiette pasta al dente according to package instructions. Reserve about ¼ cup of pasta water before draining
While the tomatoes are cooking, place saffron threads in a small bowl with the hot pasta water. Let steep for 10 minutes to release the flavor and color.
Add creme fraiche (or heavy cream) to the tomato mixture in the skillet. Stir to combine.
Using an immersion blender, blend the sauce in the skillet until smooth. Alternatively, transfer the mixture to a blender, blend, and return to the skillet.
Add drained lump crab meat to the skillet with the smooth tomato cream sauce. Stir gently to combine.
Pour in the saffron-infused water along with the threads. Keep the sauce on low heat, stirring occasionally.
Taste and season with kosher salt as needed, keeping in mind the natural saltiness of the crab meat.
Add the cooked pasta to the skillet with the creamy crab sauce. Toss gently to coat the pasta evenly. If the sauce appears too thick, gradually add some of the reserved pasta water until desired consistency is achieved.
Divide the creamy crab pasta among serving plates. Garnish with chopped chives for a fresh finish and an extra burst of flavor.