Sauté the Mushrooms: Begin by cooking your mushrooms in a pan over medium heat until all the liquid has evaporated. This step intensifies their flavor—so don’t rush it! Once fully cooked down, set them aside to cool.
Blend the Base: In a mixing bowl, combine the cooled mushrooms with the walnuts, miso paste, cornstarch, onion powder, garlic powder, paprika, and 1½ cups of water. Using an immersion blender, blend everything together until the mixture is completely smooth and liquidy.
Thicken the Pâté: Pour the blended mixture into a small pot and warm it gently over low to medium heat. Stir continuously to prevent sticking, and cook until it thickens into a rich, paste-like texture. This should take about 8–10 minutes.
Fill the Jars: Spoon the thickened pâté evenly into clean, sanitized jars. Let them cool completely on the counter while you prepare the finishing touch: the jelly topping.
Make the Citrus-Peppercorn Jelly: In a separate pot, combine ½ cup of water with the agar agar powder. Bring to a boil while stirring constantly to prevent clumping. Reduce the heat to medium, then add a few peppercorns and thin slices of lemon (or orange if you prefer), along with the juice from the remaining lemon half. Let it simmer for a minute or two, then remove the citrus slices.
Top and Chill: Place one or two citrus slices on top of each jar of cooled pâté. Carefully pour the hot agar mixture over the top to create a thin jelly layer. This not only seals in the flavor but helps preserve the pâté. Transfer the jars to the fridge to chill and set.