Soak sweetbreads in cold water for 1 hour to remove impurities.

Drain sweetbreads and simmer in fresh cold water until boiled. Drain again.

Remove the outer skin from the sweetbreads.

Slice the sweetbreads in half.

Preheat oven to 400°F (200°C).

Brush bread slices with clarified butter and toast for 15 minutes until golden brown.

Remove bread from oven and brush edges with beaten egg white for better parsley adhesion.

Coat the edges of the bread with chopped parsley.

Melt butter in a saucepan over low heat.

Add flour to the melted butter and stir continuously to create a roux. Cook for 1 minute.

Gradually add veal stock, whisking to avoid lumps. Bring to a boil.

Season with salt, pepper, and bay leaves. Reduce heat to simmer and cook for 5 minutes.

Heat clarified butter in a frying pan over medium heat.

Add mushrooms and parboiled onions, sautéing gently for 2 minutes until lightly browned.

Season with salt, pepper, and lemon juice.

Add the sautéed mushrooms and onions to the sauce.

Add sliced sweetbreads to the sauce and simmer for 5 minutes.

In a separate bowl, whisk together 2 tablespoons of cream and egg yolks.

Add a dash of hot sauce to the egg/cream mixture.

Slowly pour the egg/cream mixture into the sauce while stirring constantly to prevent curdling.

Remove bay leaves from the sauce.

Stir in the remaining cream.

Fill the toasted bread croustades with the sweetbread mixture.

Sprinkle with parsley and paprika for garnish.