Preheat the oven to 180°C, gas mark 4. Bake the bread for 5 minutes. Carefully cut each slice in half horizontally, rub with the garlic clove and bake for 5 minutes more, turning halfway, until golden and crisp. Break into shards and set the croutons aside until needed.
Put the chopped anchovies, yogurt, 1 tbsp olive oil, the grated parmesan and lemon zest and juice in a bowl. Stir to combine and chill in the fridge until needed.
Bring the steak to room temperature. Season all over and drizzle with the remaining olive oil. Set a large non-stick frying pan over a high heat. Once hot, add the steak and cook for 3 minutes on each side, or until done to your liking. Transfer to a board, leave to rest for 2-3 minutes, then thinly slice.
Put the turnips in a bowl filled with ice-cold water for 5 minutes to crisp up. Drain well and pat dry. Brush the baby gem quarters with half the Caesar dressing.
Divide the lettuce, turnips and croutons between two plates. Top with the sliced steak, scatter over the parmesan shavings and drizzle with the remaining dressing.