Heat oven to 350 F.
In a large pot of salted boiling water, cook pasta until al dente. Drain and return to pot.
In a large skillet over medium heat, melt butter. Add garlic and cook until fragrant. Add flour and whisk to combine. Cook 1 minute.
Add milk and whisk until smooth. Simmer until thickened, 2 minutes, stirring occasionally.
Add cream cheese and stir until melted and smooth.
Add hot sauce and ranch seasoning; stir until combined.
Add cooked pasta, chicken and chives; stir until pasta is completely coated.
Top with cheddar cheese and bake at 350 F for 15 minutes, until cheese is melted. (Broil for about 5 minutes to get the cheese golden and slightly crispy.)
Garnish with chives and serve.