The idea of shoving lovely, tender shrimp into a little pot may seem a bit backwards to some, but once you've tasted the gently seasoned butter and lovely tender shrimp you'll understand why this classic British dish is coming back into style. Most British versions of this recipe call for brown shrimp, which are the intensely flavorful small shrimp found in the UK, and are difficult to find in the US. Substituting larger shrimp, and then coarsely chopping them works fine as a substitution.
The concept of 'potting' is similar to confit—which is to say, preserving the product in fat. The simple difference is that potted foods are generally set in clarified butter, whereas confit is generally set in animal fat. Potted shrimp are a popular use of this technique (shrimp and butter is a great combination) but this technique is also used for many off cuts of meats such as chicken livers.
If I'm being truthful, the most arduous part of this recipe is clarifying the butter, but even that is just a waiting (and skimming) game. Once that is done the recipe comes together quickly, and then it's off to the fridge to set.
Having fresh, hot toast on hand is essential when serving potted shrimp. What you're looking for is the butter beginning to soften and melt once it hits the toast. A few big pints of lager and a green salad and you've got a lunch to be proud of.