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1
In a large skillet, heat 2 tablespoons of the oil over medium heat until it slides easily in the pan, 2 to 3 minutes.
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2
Add the onions and cook, stirring occasionally so they don't stick to the pan, until they are soft and caramelized, about 20 minutes.
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3
Spread the onions out over the surface of the pan.
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4
Remove from the heat and lay the cheese on top of the onions, letting it melt.
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5
To make a jus, in a small saucepan, bring the stock to a simmer over medium heat.
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6
Remove from the heat and stir in the balsamic glaze.
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7
Cover the pan to keep the jus warm.
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8
Season the meat on both sides with the salt and sugar.
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9
In another large skillet, heat the remaining 2 tablespoons oil over high heat.
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10
Add half the medallions, or as many as will fit in a single layer, and sear them until they are caramelized, 1 to 1 1/2 minutes per side.
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11
Cook the remaining medallions in the same way, adding more oil and letting it get hot before adding the meat to the pan.
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12
Meanwhile, without opening them, toast the baguettes so that the outsides, top and bottom, are hot and crispy.
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13
Halve the baguettes horizontally, leaving them hinged on one side.
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14
To assemble the sandwiches, lay 3 medallions on the bottom of each baguette.
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15
Top with the onions and cheese, dividing them equally among the sandwiches.
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16
Drizzle 1/4 cup of the jus on the inside top half of each baguette.
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17
Close up the sandwiches and you're good to go.
