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1
Place the beef in a medium bowl, sprinkle with the salt, and lightly mix with your hands until thoroughly blended.
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2
Cover and refrigerate for at least 4 hours or up to overnight.
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3
To make the mayonnaise, in a food processor, combine the egg, mustard, lemon juice, and salt and process until thoroughly blended.
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4
With the motor running, slowly drizzle in the oils to make a thick emulsion.
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5
Transfer to a small bowl, cover, and refrigerate until ready to use or for up to 5 days.
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6
To make the pickled onions, toss together the onions and salt in a medium bowl.
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7
Combine the vinegar, water, and sugar in a small saucepan and bring to a boil, stirring to dissolve the sugar.
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8
Pour the hot mixture over the onions, stir well, and set aside for at least 1 hour or up to overnight.
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9
To cook the burgers, prepare a medium-hot grill or film a large, heavy skillet, preferably cast iron, with oil and place over medium-high heat.
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10
Divide the ground beef into 6 equal portions, and form each portion into a patty about 1/2 inch thick.
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11
Place the patties on the grill directly over the heat source or in the hot skillet.
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12
Cook, turning 2 or 3 times, until medium-rare, about 9 minutes, by either method, or until as done as you like.
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13
Toast the ciabatta, cut sides down, on the grill or cut sides up in a toaster oven for 1 to 2 minutes until beginning to turn golden.
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14
Sandwich a patty between bun halves and serve at once.
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15
Pass the mayonnaise, pickled onions, and lettuce on the side to be added as desired.
