Preheat oven to 375°F (190°C).

Butter bread slices.

Cube the buttered bread.

Slice sharp cheese into thin pieces.

Butter a casserole dish.

Layer cubed bread and cheese slices in the buttered casserole dish.

In a separate bowl, whisk together eggs, half and half, brown sugar, onion, pepper, paprika, mustard, salt, and cayenne pepper.

Pour the egg mixture over the bread and cheese layers.

Gently press down on the bread to ensure it's soaked in the egg mixture.

Bake in the preheated oven for 35-40 minutes, or until the souffle is puffed and golden brown.

Let stand for a few minutes before serving.