Let’s create this beautiful Vanilla Bean Pistachio Cake! First, prepare the oven and pans. Preheat your oven to 350°F (175°C). Grease and line two 9-inch round cake pans with parchment paper circles, then grease the parchment as well. Set aside.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until well combined. Set this dry mixture aside.  

In a large bowl (or the bowl of your stand mixer with the paddle attachment), beat the softened unsalted butter and granulated sugar together on medium-high speed until light in color and fluffy in texture, about 3-5 minutes. Scrape down the sides and bottom of the bowl. Add the room temperature eggs one at a time, beating well after each addition until incorporated.

Now, prepare the vanilla bean. Place the bean on a cutting board. Using the tip of a sharp paring knife, carefully slit the bean lengthwise from end to end, cutting through only the top layer. Open the bean like a book. Using the back (dull side) of the knife blade, scrape down the length of each half of the pod to collect the tiny black seeds (vanilla caviar). Add these scraped seeds directly into the butter-sugar mixture. Add the vanilla bean paste (or pure vanilla extract) as well. Mix briefly on low speed to incorporate the vanilla.

Alternate adding the dry ingredients and the room temperature milk to the wet ingredients, beginning and ending with the dry mixture. Add about one-third of the dry mixture and mix on low speed until just barely combined. Add about half of the milk and mix on low until just combined. Repeat with another third of dry, the remaining half of milk, and finish with the last third of dry ingredients. Mix only until the last streaks of flour disappear. Do not overmix.

Divide the batter evenly between the two prepared 9-inch cake pans. Smooth the tops gently. Bake for about 25-30 minutes, or until the tops are golden brown, feel slightly firm to a light touch, and a wooden toothpick inserted into the center comes out clean.

Remove the cakes from the oven and let them cool in the pans on wire racks for about 10-15 minutes. Then, carefully invert the cakes onto the racks, remove the parchment paper, and let them cool completely before frosting.

While the cakes cool, make the Pistachio Frosting. In a large bowl (or stand mixer bowl with paddle), beat the softened unsalted butter on medium-high speed until very light, pale, and fluffy – about 5 minutes. Scrape the bowl well. Add the dry instant pistachio pudding mix and the teaspoon of pure vanilla extract. Blend on low speed until combined, then beat on medium speed for about a minute until smooth.

Turn the mixer speed down to low. Gradually add the sifted powdered sugar, about 1 cup at a time, alternating with additions of the milk. Start with about 4 tablespoons of milk total, adding it slowly as you add the sugar. Mix on low until just combined after each addition.

Once all the sugar and initial milk are incorporated, increase the mixer speed to medium-high and beat for a full 5 minutes. This makes the frosting exceptionally light and fluffy. Check the consistency – if it’s too stiff, beat in more milk, just 1 teaspoon at a time, until it reaches a smooth, spreadable consistency. If it’s somehow too thin (unlikely with this much sugar unless butter was too soft), beat in more sifted powdered sugar.

Time to assemble! Place one completely cooled cake layer onto your cake stand or serving plate (using a turntable makes the decorating step easier). Spread about 1 cup of the pistachio frosting evenly over the top, stopping about 1/2 inch from the edges. Carefully place the second cake layer on top.

Use a generous amount of the remaining frosting to cover the top and sides of the cake. Smooth it relatively evenly with an offset spatula. Reserve about 1 cup of frosting for the decorative piping later.

Now, for the textured finish described: Hold your clean offset spatula gently against the frosting near the bottom edge of the cake. Keep the spatula relatively still while slowly spinning the cake on the turntable (or carefully rotating the plate). The spatula blade will create horizontal lines or grooves in the frosting. Slightly lift and move the spatula up a bit and repeat the process, creating parallel textured rows all the way up the sides of the cake until you reach the top edge. Smooth the top edge carefully.

Transfer the reserved 1 cup of frosting to a piping bag fitted with a large star tip. Pipe large rosettes or swirls decoratively on top of the cake. Finally, sprinkle the top generously with chopped pistachios, if desired. Chill the cake briefly to help the frosting set before slicing.