Preheat oven to 375°F. Grease a large baking dish and set aside.
In a large pot, melt 1 tbsp of butter. Add shrimp and cook until pink, about 2 minutes on each side. Remove shrimp from pot and set aside.
Melt 4 tbsp of the butter in a large pot over medium heat. Add onions and spices, cooking until onions are softened, about 5 minutes. Slowly add flour, whisking until it forms a thick paste, about 1 minute. Whisk in white wine and cook 1-2 minutes.
Add milk and slowly bring to a boil while whisking. Reduce heat and simmer until sauce begins to thicken. Add cheddar, gruyere and parmesan, stirring all ingredients together until cheese melts. Remove from heat.
Stir in Dijon mustard, salt, pepper, nutmeg, cayenne, and chives and mix well. Fold in shrimp and pasta. Pour everything into baking dish.
In a small pot, melt remaining 3 tbsp of butter. Remove from heat, add breadcrumbs and mix well. Spread breadcrumbs on top of mac and cheese evenly. Bake mac and cheese (uncovered) for 20-25 minutes, or until top is golden brown and sauce is bubbling. Remove from oven and let cool slightly before serving.
Click on the time in the instructions to start a timer!Make sure the pasta is only cooked until al dente (or else it will come out mushy!).