Wash and dry all produce. Preheat oven to 400 degrees. Peel shallot, then thinly slice into rings. Cut ciabattas into 1-inch cubes. Halve tomatoes lengthwise. Strip thyme leaves from stems until you have 1 tsp; reserve remaining sprigs. Thinly slice garlic, then place in a large bowl with 2 TBSP olive oil and microwave on high until fragrant, about 30 seconds.

Add ciabattas and stripped thyme leaves to bowl with garlic mixture. Toss to coat. Spread on one half of a baking sheet. Place shallot on other half and toss with a drizzle of olive oil. Season both with salt and pepper. Bake in oven until shallot is soft and ciabattas are toasted, 8-10 minutes.

Heat a drizzle of olive oil in a large pan over medium-high heat. Pat steak dry with a paper towel. Season all over with salt and pepper. Add to pan and cook until browned on bottom, 2-4 minutes. Add 1 TBSP butter and thyme sprigs. Flip steak, tilt pan toward you, and continuously spoon butter over steak until cooked to desired doneness, 2-4 minutes more.

Remove steak from pan and set aside on a plate to rest. Discard thyme sprigs. Lower heat under pan to medium low, then stir in 1/3 cup water, demiglace, and 1 TBSP balsamic vinegar (we sent more). Simmer until slightly thickened, about 2 minutes. Add 1 tsp butter and stir until melted. Season with pepper.

Discard any pieces of garlic stuck to ciabattas. Toss tomatoes in another large bowl with remaining balsamic vinegar and 1 TBSP olive oil. Season with salt and pepper. Add shallot, ciabattas, arugula, and any resting juices from steak on plate. Season with salt and pepper. TIP: Add a drizzle of olive oil if salad seems dry.

Thinly slice steak against the grain. Divide panzanella between plates, then top with steak. Drizzle with sauce and serve.