Preheat the oven to 400°. Add the tomatillos and seeded serrano peppers to a sheet tray lined with parchment paper along with 4 ears of corn on the cob.
Next, add the serrano peppers to a blender along with the tomatillos, pepitas, cumin, sugar, dry oregano, lemon juice, and cilantro leaves and puree on high until smooth and set aside.
Shuck the cooked corn and slice the corn off the cob. Note: Wait a few minutes to shuck as it will be hot. Season the pork on all sides with salt and pepper.
Sear it over high heat in a large cast-iron pot with a lid with 1 tablespoon of olive oil until golden brown on all sides. Set the pork aside on a plate.