• Read through the recipe twice before starting and measure all your ingredients in advance. Go back and watch my full video tutorial, read my expert tips and extended instructions with photos. This recipe is made in steps and not all at once.

Make the pastry cream.

• The pastry cream needs a few hours to cool down and set. I recommend making it the night before or the morning of. In a large bowl, whisk together egg yolks and sugar until for 1-2 minutes until light yellow in color and all the sugar is dissolved. Then, add corn starch and whisk until smooth and thick.
  6 egg yolks, 3/4 cup granulated sugar, 6 Tablespoons corn starch
  
• Heat milk and vanilla over medium/low heat until steaming. Do not simmer! We want the milk just warm enough.
  1 ½ cups whole milk, 2 vanilla bean pods, scrapped
  
• While whisking the egg mixture continuously, slowly add the warmed milk into the egg mixture. Whisk until fully combined.
  
• Pour the whole mixture through the sieve back into the pot. Whisk continuously for 5 to 7 minutes until thickened. Be patient! Once it starts to stick to the pot, whisk vigorously to smooth out the mixture. You might see some small clumps and that's okay. It will be thick! Remove from the heat.
  
• Add butter and whisk together until combined. It may separate at first but it will come together as you whisk.
  4 Tablespoons unsalted butter
  
• Press down the surface and directly cover the custard with plastic wrap to prevent a top layer of dry skin from forming. Allow it to cool at room temperature or in the fridge for 4 to 5 hours.

  Note: If you'd like to, make the pastry cream ahead of time and refrigerate for up to one day. Before using, give it a whisk to smooth out the texture as it will have set into a firm, thick custard.

Make the choux pastry.

• Preheat the oven to 375°F / 190°C. In a medium saucepan, combine butter, water, sugar and salt. Heat until butter is melted and mixture is simmering.
  1 cup water (may substitute with 1/2 cup milk and 1/2 cup water), 1/2 cup unsalted butter, 1 Tablespoon granulated sugar, Pinch of salt
  
• Add the flour all at once. Stir vigorously with a wooden spoon or rubber spatula until the mixture forms into a smooth ball and pulls away from the sides. There should be film sticking on the bottom of the pan. That's when you know it's ready. Remove from the sauce pan into a bowl. Set aside to slightly cool for 5 minutes. It should still be warm to the touch.
  1 cup all-purpose flour
  
• Use an electric hand mixer or a stand mixer with a paddle attachment, to beat one egg at a time until fully combined. By the last egg, the dough will become smooth, shiny, sticky and thick.
  3 large eggs
  
• Prepare the springform pans with parchment paper on the bottom and butter the sides with softened butter. Equally divide the dough into two springform pans. If you only have one pan, bake one layer at a time.
  
• Spread the dough evenly, all the way to the corners. Then, use the back of a spoon to create pockets and uneven divots of dough that lift up. 
  
• Bake for 28-30 minutes until puffy and light, golden brown. Cool for 5 minutes in the pans, then remove and set aside to completely cool on a wire rack.
  

Prepare the filling.

• Only when you're ready to assemble and serve the éclair cake should you make the whipped cream and complete this step. Place the heavy whipping cream and powdered sugar in a large mixing bowl. Use a hand mixer or stand mixer and whisk until stiff peaks form.
  1 ½ cups heavy whipping cream, 2 Tablespoons powdered sugar
• Use the electric mixer to whisk the pastry cream until smooth and comes together. At first, it will resemble crumbly dough but as it is mixed, it returns to its original, thick texture. Then, fold in 1/3 of the whipped cream at a time.
  

Assemble the cake.

• Line the edges of spring form pan with parchment paper for easy release of the cake. Add one éclair layer, then all the filling and top with the final éclair layer. Make sure the filling is spread evenly to the edges of the pan.
  
• Cover the entire cake with plastic wrap and refrigerate for at least 2 hours in the springform pan. Keep in the refrigerator until ready to slice and serve. This cake is meant to be cut into thick slices in order to maintain the layers and cream in place. Don't worry, you'll thank me later for that. Best served chilled.