In a large skillet over medium-high heat, melt the butter until it begins to bubble. Add the shrimp and cook for about ninety seconds, shuffling the shrimp around so they cook uniformly.
When the shrimp are pink, add the Cognac over all the shrimp and bring to a light boil. If you know what you're doing and have a fire extinguisher nearby, touch a flame to the skillet contents. A convincing burst of fire will erupt, then die down. (If you decided not to flambee, just let the Cognac evaporate until nearly gone.)
Lower the heat to medium, then add the cream. Stir in the paste of mustard and the salt and bring to a very low boil. Cook, stirring, until the sauce thickens to a pleasing consistency. (You'll know it when you see it.) As that point approaches, taste the sauce and add salt and Tabasco to taste.
The dish is done at this point. The current vogue is to serve this with rice, but if you do, make it a really good rice that stands on its own flavors, and spoon it on the side of the plate, just touching the shrimp and its sauce.