Pat the pork spare ribs dry with paper towels, then cut them into 2 to 3-inch individual riblets if not already done. Season generously on all sides with salt and pepper, making sure to coat evenly. Let the seasoned ribs sit at room temperature for about 10 minutes while you prepare the sauce base—this helps them cook more evenly.

Heat the oil in a large pan over medium-high heat. Add the guajillo peppers and ancho pepper (stems and seeds removed) and toast them for 2-3 minutes, stirring occasionally, until fragrant and slightly darkened—be careful not to burn them or they'll become bitter. Transfer the toasted peppers to a bowl and cover with boiling water, letting them soak for 10 minutes until softened. While the peppers soak, quarter the tomatoes and roughly chop the garlic cloves and onion half for easier blending.

Drain the softened peppers, reserving their soaking liquid. In a blender, combine the drained peppers, quartered tomatoes, garlic, and onion. Add the chicken stock, orange juice, apple cider vinegar, water, paprika, oregano, thyme, cumin, brown sugar, and bay leaves. Blend until completely smooth—this should take about 1-2 minutes. For the finest texture, I like to strain the sauce through a fine-mesh sieve to remove any pepper skin bits, which gives a silkier mouthfeel. This step is optional but worth it for authentic results.

Heat the pressure cooker on high heat and add a tablespoon of additional oil if needed. Working in batches if necessary to avoid crowding, sear the seasoned riblets for 2-3 minutes per side until deeply browned—this develops rich, savory flavors through the Maillard reaction. Don't worry about cooking them through; you're just building color and flavor. Once all ribs are seared, carefully drain off excess oil from the pot, leaving just a light coating.

Pour the sauce from Step 3 over the seared ribs in the pressure cooker, making sure the liquid covers them as much as possible. Add the cinnamon stick and stir gently to distribute the sauce evenly. Seal the pressure cooker and bring it to high pressure, then cook for 15 minutes on high heat. I find this timing gives you fall-apart tender ribs without them becoming mushy. Once the time is up, carefully release the pressure following your pressure cooker's instructions, then remove the lid and discard the bay leaves and cinnamon stick.

If the sauce looks watery, you can reduce it by simmering uncovered on medium-high heat for 5-10 minutes, stirring occasionally, until it reaches your desired consistency. The ribs should be very tender and easily pulled from the bone. Serve immediately over steamed rice, allowing the rich, complex sauce to soak in. Taste and adjust seasonings if needed before serving.