Cut the pumpkin in half and use a spoon to scoop out and discard the seeds. Cut out the stem and carefully peel the pumpkin. Reserve a few larger strips of pumpkin peel. Slice the peeled pumpkin halves into roughly ½-inch (1.5 cm) cubes. A pointy corner or rounded side here or there is fine.
Place the pumpkin cubes in a bowl. Stir the salt into 5 cups (1175 ml) of the water until dissolved and pour over the pumpkin. Use a small plate or other food-safe, nonmetallic weight to submerge the pumpkin pieces in the brine. Allow to soak for 12 to 24 hours. After brining, drain, pat dry, and place in a large bowl. In your smallest saucepan, bring the remaining ¾ cup (175 ml) water and the rice flour to a boil over medium-high heat, whisking constantly. Reduce the heat to medium and continue whisking until the mixture thickens, about 2 minutes. Remove from the heat and set aside to cool to room temperature and thicken further.
While the rice paste is cooling, trim the leek and slice it into 1/8-inch (3 mm) or thinner rings. Place the rings in a small bowl and cover with water. Set aside. Cut the stems off the collards and lay the leaves on top of each other. Roll them up and cut into ½-inch (1.5 cm) strips. Place the strips in the bowl with the pumpkin. Once the rice paste is cool, place it in the bowl of your food processor along with the garlic, ginger, gochugaru, red pepper flakes, fish sauce, onion, and carrot. Process until the mixture is relatively smooth.
Remove the leek from the soaking liquid, being careful not to disturb any grit at the bottom of the bowl, and place it in the bowl with the pumpkin and collard pieces.
Put on your kimchi gloves. Scoop the blended rice paste into the bowl with the vegetables and use your hands to mix the ingredients together and to coat the vegetables. Once the ingredients are well mixed, remove the glove from your nondominant hand and use that hand to hold a clean quart (900 g) jar. Pack the mixture in the bowl tightly into the jar, leaving an inch (2.5 cm) of headspace at the top of the jar. Wipe the rim of the jar with a clean, damp cloth to remove any paste that may have clung there. Using your preferred method, weight the kimchi down to submerge it under a thin layer of paste and cover your jar. You may also choose not to use a weight for this recipe, since kimchi is not prone to surface issues.
Ferment at room temperature from 6 days to 3 weeks. Remove the weight, secure the lid, and place the jar in the fridge.
Yield: 1 quart (900 g)
Excerpted from Ferment Your Vegetables (Fair Winds Press, 2015)