Salisbury Steak with Garlic Mashed Potatoes and Corn

For the garlic mashed potatoes:

Russet potatoes : 4 large (peeled and cubed)
Garlic : 3 cloves (peeled)
Butter : 4 tablespoons
Milk or heavy cream : ½ cup
Salt and pepper : to taste
For corn:
Corn kernels : 1 ½ cups (fresh or frozen)
Butter : 2 tablespoons
Salt and pepper : to taste
Optional ingredients :

Fresh parsley : chopped, for garnish
Chopped green onions : for more flavor
Instructions :
1. Prepare the Salisbury steaks :

In a large bowl, combine ground beef, breadcrumbs, egg, Worcestershire sauce, ketchup, mustard powder, salt and black pepper. Mix until well combined.
Shape the mixture into 4 oval patties.
In a large skillet, heat the olive oil over medium-high heat. Add the patties and cook for about 4 to 5 minutes on each side until golden brown. Remove the patties and set aside.