In a large pot, combine the pears, orange quarters, cinnamon sticks, star anise, cardamom pods, nutmeg, brown sugar, lemon juice, and water.
Bring to a gentle boil over medium-high heat, then reduce to low and simmer uncovered for approximately 2 hours, stirring occasionally, until the pears are very soft and the liquid is fragrant.
Remove from heat and discard the orange quarters and whole spices. Using a slotted spoon, transfer the softened pears to a blender along with some of the cooking liquid. Blend until smooth, adding more liquid as needed.
Strain the blended pears through a fine-mesh strainer into a large bowl or pitcher, pressing gently to extract the juice. Stir in additional strained cooking liquid until you reach your desired consistency.
Stir in the vanilla extract and taste, adjusting sweetness if needed. Allow to cool completely before transferring to airtight bottles or jars.
Store in the refrigerator for up to 3–4 days, or freeze for longer storage.