In a medium skillet, melt unsalted butter over medium heat, then add the finely chopped onion. Sauté for 4-5 minutes until the onion turns translucent.

Add the finely chopped cremini mushrooms and minced garlic to the skillet. Cook for an additional 5 minutes, stirring occasionally until the mushrooms are tender.

Stir in the dry sherry, salt, and black pepper into the skillet. Allow this mixture to simmer for about 10 minutes.

Preheat your oven to 350°F (175°C) for gently baking the pâté.

In a large mixing bowl, combine the cream cheese, eggs, chopped spinach, and finely chopped walnuts. Mix thoroughly.

Fold the cooled mushroom mixture into the cream cheese combination, gently mixing until evenly combined.

Grease a loaf pan with butter, then transfer the mixture into the pan, smoothing the top with a spatula.

Place the loaf pan in a larger baking dish, filling it with hot water until it reaches halfway up the sides of the loaf pan.

Carefully bake for 1 hour and 15 minutes until the edges are set but the center remains slightly wobbly.

Once done, let it cool at room temperature and chill before slicing for the best texture.