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1
For the meat: Mix garlic, rosemary, balsamic vinegar, wine, olive oil, and black pepper to taste in a self-sealing plastic bag or a shallow dish.
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2
Add the meat, turning to coat, and cover or seal.
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3
Refrigerate for several hours or overnight.
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4
Prepare an outdoor grill with a hot fire for indirect grilling.
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5
For the marmalade: On a large sheet of heavy-duty aluminum foil (or a doubled piece of regular), toss the onions with the rest of the marmalade ingredients.
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6
Bring edges of foil up and crimp closed.
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7
Place package on the edge of the grill (over medium-high heat).
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8
Cook, turning the sealed package every now and then so the onions cook evenly until meltingly tender, about 45 minutes.
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9
Remove the meat from the marinade, pat it dry, and season generously with salt and black pepper to taste.
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10
Lightly oil the grill and sear the meat over high heat for 5 minutes.
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11
Then rotate it (don't turn it over yet) about 45 degrees from its original spot on the grill.
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12
Once you've made your grill mark, flip and repeat on the other side.
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13
Move the steak to the cooler side of the grill, cover with an aluminum pan, and cook, rotating (not flipping) periodically, until a meat thermometer inserted into the thickest part of the steak registers 125 degree sF, about 15 to 20 minutes.
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14
Let steak rest on a cutting board about 10 minutes.
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15
For the toast: Meanwhile, sprinkle garlic cloves with salt.
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16
With the flat side of a large knife, mash and smear garlic mixture into a paste.
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17
Mix with the butter.
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18
Lightly oil the grill, place bread over direct heat, and toast on both sides until golden brown, about 2 minutes total.
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19
Remove bread from grill and spread generously with the garlic butter.
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20
Thinly slice steak against the grain on an angle.
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21
Top toasts with onion marmalade, arugula, and sliced meat.
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22
Serve open-faced with mustard and/or horseradish.
