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1
Place the potatoes in a sauce pot with water to cover by one inch.
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2
Bring to a boil over high heat, add some salt, and cook the potatoes until tender, 12 minutes.
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3
Turn off the heat.
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4
Drain the potatoes and return to the pot, and let them sit for a minute to dry out.
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5
Add the butter and a splash of milk or half-and-half.
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6
Add the egg and mash mixture with a potato masher or fork.
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7
Add the chives and salt and pepper and continue to mash until fairly smooth.
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8
Preheat broiler or grill.
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9
While the potatoes are cooking, start on the burgers.
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10
In a bowl, combine the sirloin, worcestershire, and parsley.
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11
Grate about 2-3 tablespoons of the onion directly into the bowl; wrap up the remainder of onion and save for another use.
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12
Season the meat with salt and pepper and mix to combine.
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13
Score the meat with the side of your hand into 4 equal portions.
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14
Form each portion into a patty about 1-inch thick and press a slight indentation into the center of each.
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15
This dent will promote more even cooking and prevent the burger from bulging.
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16
Preheat a large skillet over medium-high heat with about 2 tablespoons of olive oil.
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17
Once the oil ripples, add the patties and cook on each side for 7-8 minutes for rare to medium-rare; 11-12 minutes for medium to medium well-done, turning once.
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18
Use the same timing if cooking on a grill.
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19
Split the kaiser buns and toast lightly under the broiler for just a minute, if desired.
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20
To build the burger, slather the bun bottoms with mustard and top with watercress or lettuce.
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21
Place the burger next and the put a mound of the mashed potatoes on top of each.
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22
Put top of bun over potatoes and enjoy.
