Tear 6 large butter croissants into uneven bite-size pieces and spread them in a 9×13 ceramic baking dish. Keep the pieces loose with natural gaps. Work at 375°F later and allow 10 minutes for the torn pieces to absorb flavor after the egg mixture is added. (I tried smaller pieces first and they turned soggy faster. Larger chunks keep the layers better.) You'll see flaky layers with soft centers and crisp edges. The smell should stay buttery and fresh. Miss this size balance and the casserole loses its texture. Even pieces soak evenly because the croissant layers need room to hold the custard.

Whisk 8 large eggs with 2 cups whole milk, 1 teaspoon salt pepper and thyme in a large clear glass mixing bowl for 2 to 3 minutes. Pour the mixture slowly over the croissant pieces and press gently with a spatula so the liquid reaches the lower layers. Let it rest for 15 minutes before baking at 375°F. The croissants should look soaked but not flooded. You'll notice the top becomes soft and glossy while the herbs smell fresh. Skip the rest and dry spots can remain inside. Resting gives the egg mixture time to settle through the flaky layers.

Scatter 1 1/2 cups shredded sharp cheddar evenly over the soaked croissant mixture and bake at 375°F for 30 to 35 minutes. Cover loosely for the first 20 minutes then uncover so the top can brown. Use a gentle folding motion with a spatula before adding cheese to keep the layers connected. The surface turns golden and the cheese melts into small pools between the croissant pieces. You'll smell the toasted butter notes when it nears the finish. Go past 35 minutes and the edges can become dry. Baking at 375°F lets the center set before the top overbrowns.

Remove the baked casserole from the oven and rest it for 10 minutes at room temperature before slicing. Cut through the uneven layers with a sharp knife and transfer one portion to a white plate. Keep the pieces natural rather than forcing clean squares because the flaky croissants separate differently. The inside should show soft egg layers with melted cheese and browned croissant edges. You'll hear a light crust crack when the top is cut. Skip this rest and the filling may slide apart. Resting 10 minutes helps the egg custard hold its structure.