Let’s bake this beautiful cake step-by-step:

Make the Cake Layers:

1. Preheat and Prep Pans: Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. Line the bottoms with parchment paper rounds.
2. Combine Dry Ingredients: In a bowl, whisk together the flour, baking powder, baking soda, and salt until combined. Set aside.
3. Cream Butter and Sugar: In another large bowl (or stand mixer bowl), beat the softened butter and sugar together until light and fluffy.
4. Add Eggs: Add the eggs one at a time, beating well after each addition until blended.
5. Add Vanilla: Mix in the scraped vanilla bean seeds and the vanilla paste (or extract).
6. Alternate Wet and Dry: Add the dry ingredients and the milk alternately to the wet ingredients, beginning and ending with the dry ingredients. Mix on low speed just until combined after each addition. Do not overmix.
7. Bake: Divide the batter evenly between the prepared cake pans. Bake for about 25-30 minutes, or until golden brown and a toothpick inserted into the center comes out clean.
8. Cool: Remove from oven and let cool in the pans on cooling racks for about 10 minutes, then turn the cakes out onto the racks to cool completely.

Make the Pistachio Frosting:

1. Beat Butter: In a large bowl (or stand mixer bowl), beat the softened butter until light and fluffy.
2. Add Pudding and Vanilla: Blend in the pistachio pudding mix powder and the vanilla extract.
3. Add Powdered Sugar: Gradually add the powdered sugar, 1 cup at a time, mixing on low speed until incorporated.
4. Add Milk: Once all the sugar is added, slowly add the milk, one tablespoon at a time, until you reach your desired spreading or piping consistency.
5. Whip: Continue to beat the frosting on high speed for about 5 minutes to make it light and fluffy.

Assemble and Decorate:

1. Level Cakes (Optional): If needed, use a serrated knife to level the tops of the cooled cake layers for even stacking.
2. First Layer: Place one cake layer on a turntable or cake stand. Spread about 1 cup of the pistachio frosting evenly over the top, stopping about 1/2 inch from the sides.
3. Second Layer: Top with the second cake layer.
4. Frost Cake: Spread the remaining frosting around the top and sides of the cake until covered, reserving about 1 cup for decorating if desired.
5. Create Texture (Optional): To make a textured cake finish, gently place an offset spatula flat against the bottom side of the frosted cake. Press lightly into the frosting and spin the cake stand around. Repeat this process in rows, moving up the cake until you reach the top edge.
6. Pipe Roses (Optional): Transfer the reserved frosting into a piping bag fitted with a large star tip. Pipe large roses on top of the cake.
7. Garnish: Sprinkle the top and/or sides with chopped pistachios, if desired.
8. Chill Chill the cake before serving.

Follow these steps for a beautiful result!