Preheat your oven's broiler to 500°F (260°C) or its highest setting.

Broil all the bread slices for about 2 to 3 minutes, until golden and crisp, but not burned.

Flip all the slices over and broil for another 2 to 3 minutes.

Turn the broiler off and allow the bread to crisp in the oven for 15 minutes.

Remove the bread from the oven and let cool.

Grate the bread slices into breadcrumbs and set aside.

In a large cast-iron skillet, melt the butter over high heat.

Add the onion and sauté for about 5 minutes, until tender.

Pour the butter and onion into a large mixing bowl.

Whisk the flour into the melted butter and onion, then slowly whisk in the milk to make a creamy sauce.

Once the sauce is smooth, whisk in the eggs, lemon juice, vinegar, and mace.

In the same mixing bowl, add the crabmeat and combine with the cream sauce, mixing lightly.

Gently fold in just enough of the breadcrumbs so that the mixture holds together.

Divide the crab mixture into equal portions (12 to 14 crab cakes).

Cover each crab cake with breadcrumbs.

Heat the ½ cup of oil over high heat in the skillet.

Once the oil is hot, place a few of the crab cakes in the skillet and reduce the heat to medium.

Cook over medium heat for about 2 minutes on each side, until browned and cooked through.

Place the cooked crab cakes on a paper towel to drain the oil.

Serve crab cakes immediately, or keep warm in a preheated oven at 175°F (80°C).