Cut the beets in half and put them into a large pan.
Fill the pan with water, until the beets are just covered.
Set the heat to high until the water boils. Then lower to medium.
Boil the beets for 35 minutes, until fork tender or you can easily stab it with a knife.
Drain the beets and let them cool.
Once the beets cool, dice them.
While dicing, you'll notice that the outer skin easily falls off-- throw the skin away.
Put the diced beets into a bowl and set aside while you make the dressing.
In a small bowl, mix the olive oil, vinegar, mustard, black pepper, and salt together. Pour the dressing on top of the diced beets. Mix and serve.