Allow steaks to come to room temperature. Season both sides with salt and pepper.
Brown steaks in cast ion skillet on both sides about two minutes per. Remove and set aside on paper towel lined plate.
Add onions plus more oil if needed. Saute onions 2-3 minutes.
Add garlic and sauté another 30 seconds.
Add paste to the skillet and mix thoroughly. Add coconut plus fish sauce. Stir, add thyme, and let simmer 2-3 minutes.
Add steaks back, cover, and simmer on low or bake at 325 degrees F until internal temperature reaches 135 degrees.
Remove the steaks and reduce gravy to desired consistency. For thicker gravy fast, make a slurry by mixing a tablespoon corn starch with ¼ cup water or the sauce and adding it back.
Add the lime juice to brighten things up.
Serve steaks over rice or mashed potatoes and top with gravy and onions.
Video
Notes
Slice sirloin against the grain for tenderness; this matters more than cook time.
Let the curry paste cook in oil for 30–60 seconds before adding liquid to avoid raw spice flavor.
Keep the simmer gentle, not aggressive; boiling will tighten the steak.
Taste at the end; balance salt with fish sauce, not more curry.
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