In a medium bowl, whisk together the grapeseed oil, soy sauce, lemon juice, Worcestershire sauce, and mustard until well combined. This creates the foundation of your marinade with balanced savory, acidic, and umami flavors. The acid from the lemon juice will begin to tenderize the steak while the oils carry fat-soluble flavors.

Add the minced garlic, brown sugar, dried thyme, and freshly ground black pepper to the marinade base from Step 1. Whisk thoroughly to combine and dissolve the brown sugar, which adds subtle sweetness and helps caramelize the steak's exterior when grilled. I find that adding the garlic last prevents it from oxidizing too much before the steak cooks, keeping its flavor bright and pungent rather than bitter.

Place your T-bone steaks in a large resealable bag or shallow baking dish and pour the completed marinade from Step 2 over them, ensuring all surfaces are coated. Refrigerate for at least 4 hours, but preferably overnight, for maximum flavor penetration and tenderizing. I like to marinate for 12-24 hours when possible—the longer contact time with the acidic components really makes a difference in the final texture and taste.