Heat a large frying pan to high heat. Add the canola oil and swirl it around in the pan to coat the bottom evenly. Sear the pork shoulder until you get a nice brown/golden color on all sides.
Once it’s golden-brown, place the pork in a slow cooker with all of the other pulled pork ingredients. Give the vegetables and beer sauce a mix.
Cover and cook at high temperature in the slow cooker for approximately 4 to 6 hours, until tender and falls apart easily.
For the special sauce, mix the mayonnaise with the apple cider vinegar, cumin powder, sugar, salt and pepper. Mix well and refrigerate until ready to use.
Remove the pork from the slow cooker to a cutting board and shred it with two forks.
Place all of the cooking liquid and the vegetables in a blender and pulse until blended. (Make sure to open the vent hole in the lid and cover with a kitchen towel to release the steam without any splashing.)
Return the pork to the slow cooker. Pour the blended vegetable mixture over the shredded pork and combine well (you might not need all of the sauce--just enough to moisten the pork and add flavor). Adjust salt and pepper as needed.
Toast the buns. Assemble the burgers with the watercress, tomato slices, pulled pork and special mayo. Serve!
Notes
Leftover fridge storage: Store leftover pulled pork, covered in the fridge, for up to 4 days.
Freezing instructions: To freeze the pulled pork, let it cool (no longer than 2 hours) and place it in double-bagged freezer bags with the air squeezed out to avoid freezer burn or you can vacuum seal it if that option is available to you. Thaw in the fridge overnight.
Sauce storage: The special sauce can be stored for up to two weeks, covered, in the fridge.
Vegetable sauce: You can reserve the unused vegetable sauce in the fridge and use it to remoisten the leftovers or even add it to mashed potatoes.
Sides: Some popular sides to serve the burgers with include fries, green salads like Caesar salad, potato salad, slaw, roasted vegetables, and grilled corn on the cob.
Sauce options: Besides my special sauce, you could try a good BBQ sauce, mayo, mustard, lime crema, HP, etc.
Prep tip: I like to chop the vegetables while the roast is searing to save some time.
Leeks: For the leeks, you only want to chop the white and light green parts. The darker green parts can be saved and used for homemade, soup stock.