Line a baking sheet with parchment paper. Add carrots, onion, and garlic and toss with olive oil.
Roast for about 30 minutes, until veggies are golden brown.
While veggies cook, cook pasta according to package directions. When pasta is al dente, drain, reserving 1 cup of the pasta water.
Transfer veggies to a blender and puree with roasted red peppers, milk, and salt until smooth.
Add sauce to the cooked pasta. Add pasta water if necessary to achieve desired consistency.
Garnish with basil or other herbs and serve immediately.
Notes
*If you don't have a high-powered blender, soaking cashews will help them blend more easily into the sauce. They can be soaked for 2-6 hours or "flash soaked" in boiling water for about 10 minutes.