Mix vegetable oil and garlic in a small bowl; set aside for 1 hour. Combine black pepper, paprika, coriander, dry mustard, white pepper, and cayenne pepper in a large bowl; set aside.

Preheat the oven to 225°F (110°C).

Cover a baking sheet with a large sheet of heavy-duty aluminum foil; coat with prepared garlic oil. Lay beef brisket on the oiled foil sheet and brush with remaining garlic oil. Cover brisket completely with pepper mixture, reserving 1 to 2 tablespoons.

Wrap brisket, fat-side up, in the sheet of foil. Place wrapped corned beef on another sheet of aluminum foil with the seam- and fat-sides down. Place double-wrapped brisket, seam-side down, on a third sheet of aluminum foil; wrap again.

Bake in the preheated oven for 6 hours.

Remove pastrami from the oven and let cool to room temperature, about 3 hours. Do not remove the foil.

Place foil-wrapped pastrami in a freezer bag or other plastic bag; refrigerate for 8 to 10 hours.

Preheat the oven's broiler and set the oven rack about 6 inches from the heat source. Line a baking sheet with aluminum foil.

Remove pastrami from the refrigerator, unwrap, and place on the prepared baking sheet. Sprinkle top with 1 to 2 tablespoons remaining pepper mixture.

Place pastrami under the broiler and cook until surface browns, 3 to 4 minutes. Remove pastrami from the oven and cut into thin slices, about 1/8-inch thick.