1. Heat a large cast-iron skillet over medium-high heat. Season steak with salt and pepper. Add oil to skillet and heat until shimmering. Add half of the steak pieces to skillet, allowing space between cubes. Cook until browned and crispy on bottoms, about 1 minute. Flip steak pieces and continue cooking until browned on other side, about 1 minute. Flip pieces again and cook until sides are browned and crispy and steak is almost medium-rare, 1 to 2 minutes. Transfer steak to a large bowl. Repeat cooking process with remaining pieces until all steak is cooked.
2. Reduce heat to medium; add 1 tablespoon butter and garlic, cook stirring constantly, until golden brown, about 30 seconds. Add vermouth and scrape up browned bits from bottom of skillet. Cook, stirring until liquid is reduced, about 1 minute.
3. Remove from heat; add butter and stir until melted and creamy. Add Worcestershire sauce and remaining 1/2 teaspoon each salt and pepper. Pour mixture over steak pieces in bowl and toss to coat.
4. Enjoy on top of mashed potatoes, blue cheese and a sprinkle of parsley.