Preheat oven to 375° F. Butter a 9 inch spring form pan or pie pan.
In a small saucepan combine the butter, water and sugar. Bring to a boil and stir until the butter is melted.
Add the flour all at once and stir with a wooden spoon until a ball forms. Put back on the heat and adjust until you hear a light sizzling noise. Cook while stirring for about 1-2 minutes just to release some of the moisture from the mixture.
Remove from the heat and let stand for 5 minutes stirring once or twice to cool slightly.
Add the eggs one at a time stirring until fully incorporated after each addition. The batter should be smooth/silky and sticky.
Spread as evenly as possible into your pan (spread over just the bottom if using spring form, spread over the bottom and up the sides if using a pie pan). Bake for 32-35 minutes or until golden brown. It will be all puffed up when it comes out of the oven but that's ok. Let it cool down until no longer warm.
Pudding Layer
While the puff is cooking start the pudding. Add the sugar and cornstarch to a medium saucepan and stir until combined. Add the milk, egg yolks, and lemon zest then whisk together until no specs of egg appear.
Cook over medium-high heat stirring constantly just until it starts to thicken, reduce heat to medium-low and continue cooking until a couple bubbles appear toward the center. Remove from the heat. Stir in the lemon juice and butter.
Push through a mesh strainer to remove the zest. Place a piece of plastic wrap directly over the top to prevent a film from forming. Allow to cool until ready to use, (you just want it to cool enough so it's not hot).
Cream Cheese Layer
Mix all ingredients together until smooth.
Assembly
Press the center of the cream puff down if its still puffed up. Spread the cream cheese evenly over the bottom. Carefully pour the pudding over the cream cheese, smooth the top and give the pan a few taps on the cupboard to even it out. Place a piece of plastic directly over the top and refrigerate for 6-8 hours hours or overnight.
Whipped Cream Layer
Beat all the ingredients together until stiff peaks form. Spread over the top of the pie. Garnish with lemon zest if desired. Slice and serve. We love serving fresh strawberries along side when we want to bump it up a notch.
Notes
If your elevation is below 2,500' do 4 Tablespoons if you're above 2,500' do 5 Tablespoons if you're somewhere in between do 4.5 Tablespoons.