Milk Chocolate and Salted Caramel Gâteau Saint-Honoré

Ingredients

• 5 tablespoons cornstarch 
• 0.1 teaspoon cream of tartar 
• 6 large egg yolk 
• 4 large eggs 
• 1 cup flour all-purpose plus more for surface (scant)
• 1 teaspoon gelatin powder unflavored
• 0.3 cup cup heavy whipping cream 
• 0.5 teaspoon kosher salt 
• 6 ounces chocolate chopped (such as Lindt or Scharffen Berger)
• 1.3 cups pastry cream chilled (from above)
• 10 servings powdered sugar 
• 28 ounce puff pastry frozen thawed (2 sheets; such as Dufour)
• 9 tablespoons sugar 
• 1 cup butter unsalted room temperature (2 sticks)
• 0.3 teaspoon vanilla extract 
• 2 cups milk whole

Equipment

• bowl
• frying pan
• baking sheet
• sauce pan
• oven
• knife
• whisk
• plastic wrap
• hand mixer
• cake form
• stand mixer
• ziploc bags
• tart form
• pastry bag
• pastry brush

Directions

1. Preheat oven to 375°F. Line 2 baking sheets with parchmentpaper. Unfold 1 puff pastry sheet on a lightlyfloured surface. Unfold second pastry sheetand place directly on top of first, forming2 layers. Press slightly to adhere. Using a10" cake pan or tart pan bottom as a guide,cut pastry with a paring knife into a 10"round.
2. Place on 1 prepared sheet.
3. Bake base until puffed and deep goldenbrown, about 30 minutes.
4. Let cool.DO AHEAD:Can be made 1 day ahead. Storeairtight at room temperature.
5. For cream puffs, preheat oven to 375°F.
6. Combine milk, butter, sugar, and salt in amedium saucepan; bring to a boil.
7. Removefrom heat and add 1 cup flour. Stir tocombine. Return to medium-high heat; stirdough vigorously until a dry film forms onbottom and sides of pan, about 2 minutes.
8. Transfer dough to a stand mixer fittedwith a paddle attachment.
9. Add eggs one at atime, incorporating fully between additions.Scrape dough into a pastry bag fitted with a1/2" tip or a plastic bag with 1/2" cut diagonallyfrom 1 corner. Pipe 1"–1 1/4"-diameter roundsonto second parchment-lined sheet (there should be 25–30 rounds). Smooth anypointed tips with damp fingertips to formrounded tops.
10. Bake for 20 minutes. Lower temperatureto 325°F and bake until golden brown anddry, 15-20 minutes.
11. Let cool completely.
12. Using a sharp knife, cut a small hole inbottom of each puff. DO AHEAD:> Can bemade 2 months ahead. Store airtight infreezer. Thaw before continuing.
13. Bring milk and 1/3 cup sugarto a simmer in a medium saucepan, stirringuntil sugar dissolves. Stir cornstarch and3 tablespoons water in a small bowl to dissolve.
14. Whisk egg yolks with remaining 1/4 cupsugar in a medium bowl.
15. Add cornstarchmixture. Gradually whisk in hot milk mixture;return to saucepan.
16. Whisk constantly overmedium heat until thick, about 2 minutes.
17. Remove from heat.
18. Add butter.
19. Whisk untilmelted and smooth. Divide pastry creamequally between 2 medium bowls (about1 1/4 cups each). Press plastic wrap directlyonto surface of 1 bowl of pastry cream.Chill until cold and reserve for saltedcaramel mousseline. Immediately use hotpastry cream for diplomat cream.
20. Add milk chocolate to hot pastry cream; stiruntil melted and smooth. Press plastic wrapdirectly onto surface of cream and let coolto room temperature.
21. Place 2 tablespoons cold water in a mediumbowl.
22. Sprinkle gelatin over; let stand for10 minutes to soften. Bring 1/2 cup cream toa boil in a small heavy saucepan.
23. Add hotcream mixture to softened gelatin mixtureand stir until dissolved. Chill just until cold,whisking frequently, about 5 minutes.
24. Placeremaining 1 cup chilled cream in a mediumbowl. Using an electric mixer, beat untilpeaks form.
25. Add gelatin mixture and beatuntil stiff peaks form.
26. Fold whipped cream into chocolatemixture in 3 additions, folding just to blendbetween additions. Cover and chill untilset, about 3 hours.
27. Stir 2 tablespoons water, sugar, and cream of tartarin a saucepan over medium-low heat untilsugar dissolves. Increase heat to medium-high;boil without stirring, occasionallyswirling pan and brushing down sides witha wet pastry brush, until deep amber colorforms, about 7 minutes.
28. Remove from heat;gradually add cream (mixture will bubblevigorously). Stir until any caramel bitsdissolve and mixture is smooth.
29. Let cool.
30. In a stand mixer fitted with a whiskattachment, beat reserved chilled pastry cream and caramel sauce at medium speed.Gradually add butter, 1 tablespoon at a time,beating until fully incorporated betweenadditions. Beat in salt and vanilla. Scoopinto a pastry bag fitted with a small tip or aplastic bag with 1/4" cut diagonally from1 corner and pipe into cream puffs. Covercream puffs and chill.
31. Set the puff pastry disk on aserving plate. Set half of cream puffs aside.Dip bottom of remaining cream puffs into
32. Chocolate Glaze and arrange in a circle,chocolate side down, around the edge ofthe pastry, leaving a 1/2" plain border. Repeatwith remaining cream puffs, layering overfirst row of puffs as if laying bricks. Spoonchilled diplomat cream into center of gâteau,spreading out to inner edge of cream puffs.Dust lightly with powdered sugar.