Step 1

Pat 2 pork tenderloins (about 2 lb. total) dry with paper towels. Season all over with 1 tsp. black pepper and 2 tsp. salt. Let sit at room temperature until ready to cook.

Step 2

Meanwhile, do some prep. Halve 2 medium red onions through the core. Trim off ends, peel, and slice into ½"-thick wedges lengthwise. Transfer to a medium bowl and set aside.

Step 3

Wash and dry 1 medium head of red leaf lettuce, then tear into bite-sized pieces. Transfer to a large bowl.

Step 4

Tear off nice looking fronds from 1 fennel bulb and transfer to bowl with lettuce. Trim a few inches from tops of stems, then remove stems from bulb. Cut bulb in half lengthwise and remove core. Thinly slice stems and bulb crosswise and add to bowl with lettuce. Chill until ready to use.

Step 5

Cut 3 Tbsp. cold unsalted butter into small pieces. Chill until ready to use.

Step 6

Heat 2 Tbsp. extra-virgin olive oil in a large skillet over medium-high until shimmering. Sear tenderloins until golden brown on each side, about 2 minutes per side, 6–8 minutes total.

Step 7

Using tongs, transfer pork to a plate. Cook onion, 1 Tbsp. extra-virgin oil, and ½ tsp. salt in same pan in a single layer over medium-high heat, tossing occasionally, until well browned and beginning to soften, about 5 minutes.

Step 8

Whisk 5 Tbsp. honey, 1 tsp. red pepper flakes (if you don’t like things spicy, cut the amount of red pepper in half, but we really love how the spiciness balances the sweetness here), 1 cup red wine vinegar, and ¼ cup water in a glass measuring cup and add to pan. (Make sure you get all that honey!) Bring to a simmer.

Step 9

Return pork to pan and cook, turning every 5 minutes and reducing heat as needed to keep sauce at a low simmer, until an instant-read thermometer inserted into the thickest part of the meat registers 140°, 12–20 minutes. (Start testing for doneness after 10 minutes; pork will cook differently depending on the size of the tenderloin you're working with. It’s important to use a thermometer in this case because it’s very easy to overcook a lean cut like this, and nobody likes dry pork!) Transfer pork to a cutting board to rest. This will lock in all the juices and let the pork continue to cook just a bit.

Step 10

Continue to cook sauce, stirring occasionally, until thick and syrupy, 3–5 minutes. Remove from heat and stir in cold butter with tongs until fully incorporated.

Step 11

Add remaining 2 Tbsp. extra-virgin olive oil, 1 Tbsp. red wine vinegar, and ½ tsp. salt to salad and toss to combine.

Step 12

Slice pork tenderloin on a diagonal. Divide among plates and spoon agrodolce sauce over. Serve salad alongside.