For the custard: Place 2 cups cream, 1/2 cup sugar, 1/2 cup coconut flakes and the vanilla seeds and pod in a medium saucepan. Whisk to combine and bring to a boil over low heat.
Meanwhile, combine the eggs and remaining 1/2 cup sugar in a bowl. In another bowl, combine the cornstarch and remaining 1/2 cup cream.
When the cream and coconut mixture comes to a boil, remove it from the heat and whisk half into the egg and sugar mixture. Then IMMEDIATELY whisk it back into the pan with the hot cream and coconut mixture. (See Cook's Note.)
Return the saucepan to medium heat and gradually whisk in the cornstarch and cream mixture. Bring it to a boil over medium-high heat to thicken the pastry cream, stirring frequently to prevent scorching. (It is necessary to bring this mixture to a boil to cook the cornstarch; if the mixture is not brought to a boil, the mixture will feel starchy and gritty. The desired outcome is the consistency of vanilla pudding. YUM!) Strain the custard through a fine mesh sieve into a bowl and chill until chilled through. (This can be done really quickly over an ice bath.)
For the tropical fruit salad: Preheat the oven to 400 degrees F. Place the macadamia nuts on a small baking sheet and toast until golden and fragrant, 5 to 10 minutes. Let cool slightly, then roughly chop and set aside.
Toast the remaining 1/4 cup coconut flakes in medium skillet over medium heat, stirring occasionally, until golden, 5 to 7 minutes. Remove from the skillet and set aside to cool and crisp.
For the whipped cream: Beat the cream, sugar and vanilla seeds in a chilled mixing bowl with a hand mixer until the cream starts to thicken and hold soft peaks.
To serve: Layer some pastry cream, pineapple, banana, starfruit, mango, whipped cream, toasted macadamia nuts and toasted coconut in 4 individual trifle dishes. Repeat the layers and top with a dollop of whipped cream, toasted macadamia nuts, toasted coconut and some fruit, including a slice of starfruit.
This process is called tempering, and it will allow you to combine boiling cream and eggs without resulting in scrambled eggs.