Melt 3 tablespoons butter in a large frypan over medium heat and add the canola oil. Stir in the celery and capsicum then cook until tender; about 5 minutes.
Add the spring onions,Tabasco and salt. Cook and stir until onions are wilted; about 3 minutes.
Stir the flour, prawns, ricotta cheese and milk into the capsicum mixture; cook and stir until the prawns turn pink; about 3 minutes. Remove from heat and cool.
Preheat oven to 220 degrees C.
Melt 125g butter in a small saucepan over medium heat. Remove from heat and keep warm.
Stack two sheets of filo on top of each other and cut into 3 strips about 7cm by 30cm. Brush the top of each strip with melted butter and place a teaspoon of the prawn mixture at one end. Fold filo pastry over the filling working back and forth from side to side to make a triangle. Seal the end closed with a little water or butter. Place triangle on an ungreased baking tray. Repeat with remaining filo sheets and filling.
Bake in preheated oven until tops are golden brown and flaky; 10 to 15 minutes. Cool on a wire rack.