Cook macaroni in salted water until al dente (slightly firm) drain and cool.
For cheese sauce, melt butter in large sauce pot add flour mix and cook for 3 minutes on low heat to make blonde roux. Slowly add cold half and half whisking in between additions to prevent lumps.
Cook sauce for 5 minutes, add heavy cream, cream cheese, smoked cheddar, Dijon mustard, fresh thyme, onion powder, nutmeg, cayenne pepper, season with salt and pepper.
Mix gruyere and 1 cup of white cheddar with cold pasta add cheese sauce mix well. Pour into greased baking dish top with rest of white cheddar.
Bake at 375 degrees for 30 minutes let stand 10 minutes before serving.