Preheat oven to 325 degrees Fahrenheit.

Coat two 8 1/2-by-4 1/2-inch loaf pans with cooking spray.

Line with parchment paper and spray the parchment paper with cooking spray.

Dust the pans with flour, tapping out any excess.

In a mixing bowl, beat the butter, cream cheese, and pistachio paste on medium speed until fluffy (about 3 minutes).

Reduce the mixer speed to medium-low.

Gradually add sugar and beat until the mixture is smooth.

Scrape down the sides of the bowl to ensure even mixing.

Beat in the eggs, one at a time, then add the vanilla extract.

Reduce the mixer speed to low.

Add the flour and salt and beat until just combined.

Fold in the chopped pistachios.

Divide the batter evenly among the prepared loaf pans.

Smooth the tops of the batter.

Bake for approximately 1 hour 35 minutes, or until a cake tester inserted into the center comes out clean.

Let the cakes cool in the pans for 20 minutes.

Remove the cakes from the pans and remove the parchment paper.

Let the cakes cool completely.

To prepare the icing, whisk together confectioners' sugar, heavy cream, and lemon juice in a small bowl until smooth.

Pour the icing through a sieve into another bowl to remove any lumps.

Use the icing immediately.

Drizzle the icing over the cooled cakes.

Sprinkle the cakes with pistachio slivers.