Spicy Cajun Onion Boil

Spicy Cajun onion boil is whole sweet onions cored and filled with butter, beef broth, Cajun seasoning, garlic powder, smoked paprika, and crushed red pepper flakes, wrapped tightly in foil, and cooked at 350-375°F for 60 to 75 minutes until the onions turn soft and swimming in spicy butter sauce. You core each onion about 1 to 1½ inches deep, stuff it with a stick of butter cut into pieces and broth, season it heavily with Cajun spices, wrap it in heavy-duty foil, and let the heat break down the onion layers while the butter and broth create a sauce inside. The onions steam in their own juices mixed with the butter and seasonings, turning tender and soaking up all that spicy flavor. These Cajun butter onions work as a side dish for steak, smoked meats, or grilled chicken, or you can chop them up and use them as a topping for burgers and brats.

The whole process takes about 75 to 90 minutes from start to finish including prep and cooking time. You prep the onions by coring them and filling each one with butter, broth, and seasonings, wrap them individually in foil, and cook them until they’re completely soft when you press them. The butter and broth create steam inside the foil packet that cooks the onions from the inside out while keeping all the flavor trapped. These foil-wrapped grilled onions beat regular grilled onions because they stay moist and develop deeper flavor instead of drying out, and you can adjust the heat level by controlling how much crushed red pepper and Cajun seasoning you use.

Ingredients

• 3 large sweet onions
• 4 oz unsalted butter (1 stick), cut into pieces
• 6 tbsp beef broth (or chicken broth / water)
• 2½–3 tsp Cajun seasoning (to taste)
• 1 tsp garlic powder (or 3 cloves minced garlic)
• ½ tsp smoked paprika
• ½–1 tsp crushed red pepper flakes
• Black pepper, to taste
• Salt, only if needed at the end

Instructions

Prep the Onions

• Peel and slice the tops off.
• Core each onion about 1–1½ inches deep.

Season & Fill

For each onion:

• Place a cut-up stick of butter per onion (about 2–3 tbsp per onion)
• Pour in 2 tbsp broth
• Season with Cajun seasoning, garlic powder, smoked paprika, red pepper flakes, and black pepper

(Hold salt until the end—Cajun seasoning already brings some.)

Wrap & Cook

Wrap tightly in heavy-duty foil.

Grill / Smoker:

• 350–375°F for 60–75 min

Oven:

• 375°F for 70–80 min

Onions should be super soft and swimming in spicy butter.

Finish Strong

• Carefully unwrap and stir everything together.
• Taste → adjust salt or Cajun seasoning.

🔥 Optional BBQ Finish:
Put the open foil onions over direct heat for 5–8 minutes to tighten the sauce and caramelize the edges.