Melt the butter over medium heat in a medium skillet until it bubbles. Saute the shallots, garlic, and green onions until limp.
Add the crawfish tails and saute until heated through. Carefully pour the brandy over the skillet contents and touch a flame to it. (If you're comfortable with flaming things and have firefighting resources.) When the flames die down (or all the alcohol boils away), stir in the tomato and the crawfish stock and bring to a boil.
Stir in the whipping cream, salt, and cayenne and heat through (but do not boil). Adjust seasonings and remove from the heat. Spoon into small ramekins and serve.
For an impressive presentation, top each ramekin with a piece of the puff pastry. Push it down around the sides to form a cap. Brush the pastry with beaten egg and bake in a preheated 400-degree oven until the top browns lightly. When your guests cut into the pastry cap, the wonderful aroma will hit them in the face.