Croquembouche is a crowd stunner served traditionally at buffets and weddings. Basically it’s cream puffs filled with a creamy centre stacked into a cone and glued together with sugar syrup that hardens and turns crispy. To go over the top you can decorate the croquembouche with spun sugar, sugared flowers or candied almonds. You can also fill the puffs with whipped cream or pastry cream.
Preheat oven to 400 degrees F. Line a large baking sheet or two smaller sheets with parchment paper.
Sift flour with salt and set aside.
Add water and pieces of butter over medium heat until mixture comes to a boil. Immediately add sifted flour mixture all at once and stir with a wooden spoon. Remove from heat and continue stirring until mixture pulls away from the sides of the pan. Return mixture to heat and stir slightly longer to dry the mixture, about 2 minutes. Remove mixture from heat. Beat in one egg at a time, stirring with a wooden spoon until mixture is shiny and falls from the spoon after each addition.Mixture will break apart after adding each egg but will become smooth again after stirring vigorously.
Spoon mixture in round heaps about 1.5 inches in diameter, spacing rounds an inch apart, on prepared baking sheet. Brush choux heaps lightly with beaten egg. Bake until golden brown and hollow sounding, about 20 minutes. Transfer to wire rack to cool.
Whip cream until soft peaks form, about 3 to 4 minutes. Add icing sugar and cocoa and whip until stiff. Mash banana with fork and add Kahlua in a small bowl. Fold into whipped cream. Cover with plastic wrap. Chill banana mocha filling in refrigerator until ready to fill puffs.
Fit a piping bag with a plain tip. Fill pastry bag with banana mocha filling. Make small hole in bottom of each puff and fill each with a little of the mocha filling.
Start the base of the croquembouche with a 7-inch diameter circle, either by using a 7-inch cake board or lightly pencil a 7-inch circle on a bigger cake board as a guide or carefully drizzle a circle with some of the sugar syrup.
To make the sugar syrup, combine sugar and water in a clean, heavy bottom saucepan. Bring to a boil slowly. Reduce heat and add corn syrup. Boil until sugar is thick and a caramel colour, about 10 minutes. (Sugar should reach the crack stage, 265 to 275 degrees on a candy thermometer.) Remove immediately from heat.
Use the parchment circle as a guide for the base of the croquembouche cone and drizzle some of the cooked sugar around the parchment circle. Place 8 puffs around the inside of the circle so they are touching one another and the sugar. Drizzle more sugar over top of puffs so they stick to one another. Sugar will be very hot so be extremely careful not to drip sugar on your hands. To create the cone shape, drizzle sugar on bottom of each puff and adhere it to the previous layer. Use 7 puffs for the next layer and continue to use hot sugar to stick puffs together. For the next later, use 6 puffs. Repeat this process until croquembouche cone is created and the last layer has 1 puff on top. If sugar syrup gets too stiff, simply place it back on the heat to melt it. Remember to work quickly as the sugar stiffens quickly. Garnish with crystallized flowers or spun sugar.