Bring the butter to room temperature to soften, then mix well with the mustard. Dampen the mashed potatoes, then wrap with plastic wrap. Microwave for 4 minutes at 600 W. Cut the cucumber into thin half-moon slices and rub a little bit of salt.
Peel and mash the cooked potatoes. Press the liquid from the cucumbers, and add the cucumbers, mayonnaise, and anchovy paste to the potatoes. Taste and season with salt and pepper (coarsely ground) if needed.
Spread the mustard-butter on one slice of bread, the potato salad on the other. Repeat with another 2 slices. Press the sandwiches lightly together and cut whatever way you like. Enjoy!
Story Behind this Recipe
I bought some anchovy paste and didn't know what to do with it, so I tried adding some to my regular potato salad.
Adjust the amount of anchovy paste to taste. The butter and anchovy paste already have salt in them, so you can make this recipe without adding additional salt if you like. I used sandwich bread, but feel free to use any kind that you like.