Preheat your oven to 350°F (177°C). Line three 8-inch round cake pans with parchment paper and spray with cooking spray.

In a large mixing bowl, combine sour cream, eggs, honey, cooking oil, and vanilla extract. Whisk until smooth and creamy.

In another bowl, whisk together flour, baking soda, baking powder, and salt. Gradually fold into the wet mixture.

Divide the batter among the prepared cake pans and bake for 24–26 minutes. A toothpick should come out clean.

Cool the cakes in the pans for 5–8 minutes, then transfer to a wire rack to cool completely. Refrigerate for about 30 minutes.

Blend shelled pistachios with heavy cream in a food processor until smooth. Beat softened butter, then mix in the pistachio paste and confectioner's sugar.

Level each cake layer by slicing them in half horizontally. Drizzle honey over each cut side.

Stack the layers, spreading buttercream and drizzling honey between each. Apply a thin crumb coat of buttercream and chill for 30 minutes.

After chilling, apply a thicker layer of pistachio buttercream. Garnish with finely diced pistachios and drizzle with honey.

Let the finished cake chill in the refrigerator for 1–2 hours before serving. Allow it to sit at room temperature for a few minutes before enjoying.