1. Cook pasta with 1 tablespoon kosher salt according to package directions, omitting additional fat. Drain in a colander over a bowl, and reserve 1 cup cooking liquid.
2. Combine 1/2 cup reserved hot cooking liquid and ricotta cheese in a food processor or blender, and process until well blended.
3. Combine hot pasta, cheese mixture, spinach, and remaining ingredients in a large bowl; toss gently to coat. Add additional cooking liquid to moisten, if needed.