Using a serrated knife, slice the croissant in half horizontally, leaving a small hinge at the back so it stays connected. Gently open it.

Layer the grated Gruyère, slices of Brie, and grated white cheddar inside the croissant. Close the croissant and press down gently with your palm to flatten it slightly.

In a small bowl, mix the softened butter, light brown sugar, and hot honey until it forms a thick, uniform paste.

Spread half of the butter-sugar paste evenly over the top exterior of the croissant.

Heat a skillet over medium-low heat. Place the croissant into the pan, paste-side down. Immediately spread the remaining paste over the upward-facing side of the croissant.

Place a heavy spatula, bacon press, or small heavy skillet on top of the croissant to weigh it down. Cook for 3 to 4 minutes until the bottom sugar is melted and deeply caramelized (watch closely so it doesn't burn).

Remove the weight, carefully flip the croissant with a wide spatula, replace the weight, and cook for another 3 to 4 minutes until the second side is candied and the cheese is fully melted and oozing.

Transfer the sandwich to a cutting board and let it rest for 2 minutes so the sugar shell can harden. Sprinkle the top generously with flaky sea salt.

Slice in half with a sharp knife and serve immediately for the ultimate cheese pull.