Poach the prawns in dry white wine or fish stock until just cooked through, 3 to 5 minutes, then drain and coarsely chop. If using crabmeat, pick over the meat removing any shell or cartilage and break the meat into chunks.
Melt 3 tablespoons butter in a medium saucepan over low heat. Add the garlic and spices and cook 1 to 2 minutes. Add the flour and stir well. Cook another minute, then stir in the cream and cook until thickened (see Note). Remove from the heat and stir in the shellfish, fresh herbs, lemon zest, and salt and pepper to taste. Let cool for about 15 minutes.
Cut the filo into strips about 12 by 3 inches. Keep the strips covered with a damp cloth or plastic wrap.
To assemble, brush a strip of filo with melted butter. Top it with another strip and brush it with butter. Place a tablespoon of the filling about 2 inches from the top of the strips and fold the top corner of the dough over the filling and to the opposite edge so that it looks like a triangle. Continue folding the dough like a flag until the entire strip is folded. Or place the filling at the top of the strips, tuck in the sides, and roll up into a cylinder. Repeat with the remaining filo and filling.
Deep fry the pastries, a few at a time, in peanut oil heated to 350°F until golden. Or bake on baking sheets in a 375°F oven until puffed and golden, about 7 minutes. Serve hot.