Slice the onion thinly. Cut the potatoes in half lengthwise, then slice into 7mm thick pieces. Soak in water and drain. Place in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 4 minutes.

Heat butter in a frying pan over medium heat. Add the onion and sauté until softened. Add the shrimp and cook until the shrimp changes color. Add flour and stir until no longer powdery. Gradually add milk, consomme, salt, and pepper, stirring until the sauce thickens.