Cover a rimmed baking sheet with heavy duty foil and set oven to broil.
Mix all of the dry spices together and set aside.
Place steaks in a gallon ziplock bag and add spice mixture.
Close bag and gently toss to evenly coat fillets.
Place steaks on baking sheet and broil 4-5” from heat for 7-9 minutes.
Flip steaks over and continue broiling for an additional 7-9 minutes, until desired temperature. (Medium = 155°, Medium Rare = 145°)
While steaks are broiling, heat a medium skillet to medium/low heat.
Melt butter with oil and sauté onions until caramelized.
When steaks are finished broiling, remove from oven and cover with foil to rest a few minutes.
Serve with caramelized onions on top.