Begin by prepping the frosting - add heavy cream to a large measuring up or medium bowl and place into the microwave for about 60-90 seconds, until hot. Add the chopped white chocolate to the warm cream and allow the mixture to sit for 2 minutes. Mix together until the white chocolate is fully mixed into the cream. (if it isn't fully melted, add back into the microwave in 10 second increments until everything is fully melted)
Fill large bowl with ice water. Place the cream mixture into the ice water and allow it to sit until it's cooled completely. (by the time that the cake is fully baked and cooled, it should be ready!)
Preheat the oven to 300 degrees F. Line a 9-inch springform with parchment paper. Set aside.
Place pistachios onto a baking sheet and toast them in the oven for 7-8 minutes, until fragrant and slightly browned. Set aside to cool.
Increase oven temperature to 350 degrees F.
In a large mixing bowl, add ricotta, oil, melted butter, sugar, and lemon zest. Mix together until combined, about 30 seconds, then add in the vanilla extract, almond extract, and eggs. Mix until everything is smooth.
Add in the dry ingredients - cake flour, baking soda, and kosher salt. Mix until combined, about 20-30 seconds.
Chop up the pistachios and add to the batter. Pour the cake batter into the prepared pan and bake for 40-50 minutes, until a toothpick inserted comes out with just a few crumbs. Allow the cake to cool in the pan.
Check the white chocolate cream mixture. If it's cold to the touch, it's ready to be whipped. Add pistachio paste and a pinch of salt. Use an electric hand mixer to whip the cream on medium speed until stiff peaks form. (if you prefer a sweeter frosting, add a 1/2 cup of powdered sugar)
Spread on top of the cooled cake and garnish with additional pistachios.
Notes
Use Room Temperature Ingredients: Bring eggs and ricotta to room temp before mixing—this helps everything blend smoothly and evenly.Don’t Overmix the batter. Mix just until everything is combined—overmixing can lead to a dense cake instead of a light, tender crumb.Toast the Pistachios before baking - it's an extra step but totally worth it! Toasting brings out even more nutty flavor.When making the frosting, make sure that the white chocolate cream mixture is cold prior to whipping. This ensures that you get a fluffy, smooth frosting.