Melt 12 tablespoons of unsalted butter in a heavy saucepan over low heat, being careful not to boil.

Skim off any foam that rises to the surface of the melted butter.

Add the crushed garlic, ground mace, freshly grated nutmeg, and powdered ginger to the saucepan.

Simmer the spices in the melted butter for 3 minutes over low heat to allow the flavors to develop.

Remove the garlic from the butter mixture.

Add the shelled small shrimp to the spiced butter.

Cook the shrimp for 2-3 minutes, until pink and cooked through.

Remove the saucepan from the heat.

Season the shrimp and spiced butter to taste with coarse salt and lemon juice.

Divide the shrimp mixture evenly into eight individual pots or ramekins, reserving the remaining spiced butter.

Melt the remaining unsalted butter in a separate saucepan, skimming off any impurities.

Pour the melted butter, along with the reserved shrimp cooking butter, over the shrimp in each pot, ensuring the shrimp are completely covered.

Refrigerate the potted shrimp overnight to allow the flavors to meld and the butter to solidify.

Serve the potted shrimp chilled with thin slices of toast.