Method

1. Combine shrimp and Cajun seasoning in a large bowl; toss well to coat. Set aside.

2. Cook pasta according to package directions. Reserve 1/2 cup cooking water, then drain. Return the pasta to the pot off the heat. Add 1 1/2 teaspoons oil and toss to coat.

3. Meanwhile, thinly slice white and light green parts of scallions diagonally; set aside. Thinly slice dark green parts of scallions; set aside.

4. Heat the remaining 1 1/2 teaspoons oil in a large skillet over medium-high heat. Add bell pepper and cook, stirring occasionally, until softened, about 5 minutes. Add the sliced white and light green scallions, garlic, butter and pepper; cook, stirring occasionally, until fragrant and softened, about 1 minute. Add flour and cook, stirring constantly, for 1 minute. Add broth and half-and-half; bring to a simmer, whisking constantly. Add the seasoned shrimp; reduce heat to medium and cook until the shrimp are just cooked through and opaque and the sauce has thickened slightly, 2 to 3 minutes, turning the shrimp over halfway through. Remove from heat.

5. Heat the pasta in the pot over low heat. Add spinach, sour cream, salt, the shrimp mixture and 1/4 cup of the reserved cooking water; stir to combine. Cook, stirring constantly and adding more cooking water, if necessary, until the sauce becomes thick and creamy, 3 to 4 minutes. Divide evenly among 6 bowls and garnish with the sliced dark green scallions. Serve immediately.