Preheat the oven to 350°F and spread the cubed bread on two baking sheets. Bake for 10 to 12 minutes, stirring halfway, until golden and slightly soft in the center.

Meanwhile, dice the onion and celery into small pieces and mince the garlic. Chop the parsley and thyme.

Melt 4 tablespoons of butter in a large skillet over medium heat. Add the onion and celery and cook for 6 to 8 minutes until softened.

Add the minced garlic to the skillet and cook for 30 seconds, stirring constantly.

Drain the oysters in a colander, reserving the liquor. Pat the oysters dry with paper towels.

Increase the heat to medium-high, add the remaining 2 tablespoons of butter, and sear the oysters for 90 seconds on each side. Remove and set aside with any pan juices.

Transfer the toasted bread to a large bowl. Add the cooked vegetables, parsley, thyme, salt, pepper, and cayenne pepper. Toss gently to combine.

Combine the reserved oyster liquor and broth to measure 3 cups. Drizzle over the bread mixture and stir until the bread is moist but not mushy. Let sit for 2 minutes.

Beat the eggs and pour over the bread mixture, stirring gently. Fold in the seared oysters and any accumulated juices.

Butter a 9x13-inch baking dish and transfer the mixture, spreading evenly. Bake at 350°F for 30 to 35 minutes until the top is golden brown.