Preheat your oven to 350°F (177°C) and prepare three 8-inch round cake pans by lining with parchment paper and spraying sides.

In a large bowl, mix sour cream, honey, cooking oil, eggs, and vanilla extract until smooth.

In another bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add to wet ingredients, stirring until just incorporated.

Divide batter among pans and bake for 24-26 minutes until a toothpick comes out clean. Cool in pans for 5-8 minutes before transferring to a wire rack.

Whip the unsalted butter until light and fluffy. Gradually incorporate the pistachio paste and vanilla, then add confectioner's sugar until the frosting is light and spreadable.

Level the cooled cake layers with a serrated knife, and slice each layer horizontally to create six layers.

On a serving platter, layer the cake starting with the first layer, spreading honey and frosting, topping with diced pistachios. Repeat for each layer.

Apply a thin layer of frosting over the entire cake to trap crumbs, then chill for 30 minutes.

After chilling, apply a final layer of frosting, smooth it out, and garnish with remaining pistachios and a drizzle of honey.

Refrigerate the assembled cake for 1-2 hours before serving to enhance flavor and texture.