Chocolate Eclair Cake

Ingredients

• Pastry Cream
• 1/2 cup sugar
• 1/4 cup cornstarch
• 2 cups whole milk
• 4 egg yolks
• 3 unsalted butter, divided
• 1 teaspoon vanilla
• Pastry Decorations
• 4 tablespoons butter
• 1 teaspoon sugar
• 1/4 teaspoon salt
• 1/2 cup water
• 1/2 cup all-purpose flour
• 2 large eggs
• Powdered sugar for dusting
• Cake Layers
• 3 cups cake flour
• 2 teaspoons baking powder
• 1 teaspoon kosher salt
• 6 tablespoons unsalted butter, room temperature
• 1/2 cup vegetable shortening
• 2 cups granulated sugar
• 5 eggs
• 3/4 cup buttermilk
• 1/2 cup vegetable oil
• 1 tablespoon vanilla extract
• Eclair Buttercream
• 3/4 cup butter, room temperature
• 3 cups powdered sugar
• 1/2 teaspoon vanilla extract
• pinch salt
• 6 tablespoons Pastry Cream
• Chocolate Ganache
• 6 ounces (60%) bittersweet chocolate, finely chopped and divided
• 8 unsalted butter, divided