Preheat your oven to 350°F (175°C) and generously grease a 9-inch round cake pan or springform pan with butter or non-stick spray.

Place the shelled pistachios in a food processor and pulse until they are finely ground into a meal, being careful not to over-process them into butter.

In a medium bowl, whisk together the all-purpose flour, ground pistachios, baking powder, and salt until well combined.

In a large mixing bowl, cream the softened butter and granulated sugar together using an electric mixer until the mixture is pale and fluffy, about 3-4 minutes.

Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next, then mix in the vanilla extract and lemon zest.

Add the ricotta cheese to the wet mixture and beat on low speed until just combined and smooth.

Gently fold the dry ingredients into the wet mixture using a spatula, stirring only until no streaks of flour remain to ensure a tender crumb.

Pour the batter into the prepared cake pan and smooth the top evenly with a spatula.

Bake in the preheated oven for 45 to 50 minutes, or until a toothpick inserted into the center comes out clean and the top is golden brown.

Allow the cake to cool in the pan for 15 minutes, then transfer it to a wire rack to cool completely.

Once fully cooled, dust the top generously with powdered sugar before slicing and serving with a fresh cup of espresso.