Begin by placing the peeled and deveined shrimp in a mixing bowl. Drizzle with olive oil and generously sprinkle Cajun seasoning over the top. Toss the shrimp until they are well-coated, ensuring every piece is flavorful. Allow the shrimp to marinate for 10 to 15 minutes.

In a large pot, bring salted water to a rolling boil. Add the fettuccini pasta and cook it for about 8 to 10 minutes, stirring occasionally until al dente. Once cooked, drain the pasta in a colander and set it aside, making sure to reserve a bit of pasta water for later use if needed.

Heat a skillet over medium heat and melt a tablespoon of butter. Add the chopped mushrooms and diced shallots to the melted butter, sautéing them for about 5 to 7 minutes. Cook until the mushrooms are tender and the shallots are fragrant, then remove the mixture from the skillet and set it aside for later.

In the same skillet, add a splash of olive oil if necessary and heat over medium-high heat. Add the marinated shrimp to the hot skillet, cooking them for about 2 to 3 minutes on each side until they are pink, slightly curled, and opaque. Take care not to overcook.

Pour the chicken broth into the skillet and increase the heat to bring it to a boil. Allow the broth to boil vigorously for 2 to 3 minutes, until it reduces to about a ¼ cup, concentrating the flavors.

In a medium bowl, whisk together the sour cream and cornstarch until smooth. Once your broth has reduced, gradually mix in the sour cream mixture, stirring continuously for a smooth blend.

Return the skillet to low heat and stir the sour cream mixture back into the skillet with the broth. Cook over low heat for a few minutes, allowing the sauce to thicken and become bubbly.

With your sauce thickened, return the sautéed vegetables, cooked shrimp, roasted red bell peppers, and capers back into the skillet. Stir everything together gently until heated through, making sure the shrimp and veggies are well-coated with the creamy sauce.

Finally, spoon the luscious shrimp and sauce mixture over a generous portion of fettuccini on plates. Garnish with freshly chopped parsley for a burst of color and flavor, and enjoy your homemade Blackened Shrimp Stroganoff.