Prepare the veggies: Slice up the onion, peel and chop the parsnip, and wash and finely slice the celery stalk. You’ll want to really make sure you slice the celery finely, otherwise you may get these strands of celery in your pate.
Clean the livers: Wash the chicken livers under running water until the water runs clear. Clean out any bits you don't like.
Sauté the veggies: Heat 2 tablespoons of butter in a large skillet over medium-high heat. Add the onion, parsnip, and celery. Sauté for about 5 minutes until the onion becomes translucent. Remove from the pan and place on a plate/bowl.
Cook the chicken livers: Add another 2 tablespoons of butter to the same pan. Add the chicken livers and sauté on medium heat for 5-7 minutes until they are slightly browned.
Simmer everything together: Add the veggies you put aside, one cup water and the bay leaf to the chicken livers. Simmer for about 20 minutes on medium-low heat, stirring often and making sure the livers are evenly cooked. Don't brown—just simmer gently. The pan should stay moist and not dry, so if you need to add more water, you can, but not too much. At the end of the 20 minutes, most of the water should have evaporated.
Test for doneness: After 20 minutes, taste a piece of celery. If it's cooked and not crunchy, remove the pan from heat and remove the bay leaf. If not, add a bit more water and continue to simmer until done.
Blend until smooth: Transfer the chicken livers and vegetables to a food processor (or use a stick blender). Blend until smooth.
Add final ingredients: Add the rest of the butter, juice of 1/2 lemon, nutmeg, and salt to taste. Blend until completely smooth and creamy.
Refrigerate and serve: Transfer to glass containers, cover, and refrigerate for a couple of hours to firm up.
Serve on toasted sourdough, seed or rye bread with a garden salad for a simple brunch, or spread some on toasted baguette slices or water crackers as a tasty appetizer. Or you can make a charcuterie board for friends or a special occasion.