Half an hour before cooking, grind the fennel and coriander seeds in a spice grinder or mortar and pestle. Rub the spice mix into the pork shoulder and season with salt. Cover and rest at room temperature for 30 minutes. Coat the bottom of a large Dutch oven with 2 to 3 tablespoon olive oil and place over high heat. Once the oil is hot, add the pork shoulder and sear on all sides until golden brown, 5 to 7 minutes per side. Watch carefully to make sure the spice rub doesn’t burn.