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1
Place bacon in the freezer for at least 5 minutes to firm up (this will make it easier to cut).
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2
Heat a large frying pan or cast iron skillet over medium heat.
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3
Remove bacon from the freezer and cut into 1/2-inch slices.
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4
Cut each slice into lardons (1/2-inch-by-1-1/2-inch pieces).
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5
Line a plate with several layers of paper towels; set aside.
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6
Add lardons to the pan and cook, stirring rarely, until browned and most of the fat has been rendered, about 10 minutes.
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7
Remove with a slotted spoon to the paper-towel-lined plate and let cool.
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8
Remove 1/2 of the bacon fat to a heatproof bowl and reserve.
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9
Return the pan to medium heat, add bread, and toss to coat in bacon fat.
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10
Cook, stirring frequently, until bread is toasted and lightly browned but not hard to the touch, about 5 minutes.
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11
Transfer to the paper-towel-lined plate with the bacon and season croutons with salt.
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12
In a large bowl, toss together bacon, croutons, spinach, and tomatoes; set aside.
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13
Return the pan to medium heat and add reserved bacon fat.
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14
Add shallots, salt, and pepper and saute until shallots are just tender, about 2 minutes.
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15
Stir in vinegar, scraping the bottom of the pan with a spatula to incorporate any browned bits into the dressing.
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16
Remove from heat and drizzle dressing over salad, toss to combine, and season with more salt and pepper as necessary.
