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1
Have the butcher cut a whole tenderloin in half so that you can purchase the thick end (they will usually cut the rest into steaks).
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2
Or you can buy a butt beef tenderloin.
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3
Salt and pepper the whole tenderloin thoroughly.
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4
Lay the bacon strips out on a clean work surface, touching each other, so they create a rectangular sheet of bacon.
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5
Lay the whole tenderloin across the bacon and carefully wrap the bacon ends over the top of the tenderloin.
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6
Secure the bacon strips by sewing toothpicks through the ends.
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7
Heat a large skillet to medium-high heat.
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8
Place the whole tenderloin, toothpick-side-down, in the skillet.
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9
Brown the bacon on all sides, turning as needed, about 10 minutes.
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10
This can be done ahead and the seared tenderloin can be refrigerated for 1-2 days prior to cooking it in the crockpot if needed.
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11
Place the beef tenderloin in a 5-6 quart crockpot and pour the pan drippings from the skillet over the top.
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12
Place the sliced onion, garlic cloves, and rosemary sprigs around it.
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13
Insert a meat thermometer in the thickest part of the whole tenderloin, then cover and turn the crockpot on low.
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14
A crockpot beef tenderloin will be perfectly medium-rare when the temperature reaches 130 F, in roughly 2-4 hours, depending on weight and thickness.
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15
Once the temperature reaches 100 F, mix the flour and sugar together in a medium bowl.
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16
Whisk the balsamic vinegar and mustard into the sugar until there are no clumps.
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Then whisk in the beef stock.
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Pour the mixture around the tenderloin, cover the crockpot and continue cooking until 130 F is reached.
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19
At 130 F, remove the whole tenderloin from the crock and cover it with foil for at least 10 minutes.
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20
The temperature will continue to rise to 135 F as it rests.
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21
If needed, allow the balsamic glaze to continue simmering until thick.
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22
To serve, remove the toothpicks and slice the tenderloin into thin rounds.
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23
Top with rich balsamic glaze!
