Bring a big pot of salted water to a boil and cook the pasta just shy of al dente. Reserve a cup of pasta water before draining—it’ll help later if the sauce needs thinning.
Heat olive oil and butter in a large pan over medium heat. Add the cubed chicken and cook for about 6–7 minutes, until golden and cooked through. Set it aside once done.
In the same pan, add shallot and garlic. Cook for a minute or two until fragrant. This step builds the flavor base of the sauce.
Stir in tomato paste and chicken stock until smooth. Lower the heat and whisk in softened cream cheese until the sauce looks silky and lump-free. Pour in the buffalo sauce and ranch dressing, mixing well. Let it bubble gently so the flavors blend into a bold, tangy, creamy sauce.
Add the cooked pasta back into the pan and stir gently to coat each piece in sauce. If the sauce feels too thick, use a splash of reserved pasta water to loosen it up.
Finally, stir in cheddar and Monterey Jack cheeses until melted and gooey. Serve the pasta hot and enjoy the creamy, cheesy, spicy goodness.