2 cups whole milk
6 large egg yolks
1/2 cup (packed) light brown sugar, pressed through a sieve
1/3 cup cornstarch, sifted
1/2 teaspoon ground cinnamon
1/8 teaspoon freshly grated nutmeg
pinch of salt
1 teaspoon pure vanilla extract
3 tablespoons cold, unsalted butter, cut into bits
3 ripe but firm bananas, sliced

To make the custard, bring the milk to a boil.  In a separate saucepan, whisk together the eggs, sugar, cornstarch, cinnamon, nutmeg and salt until blended and thick.  Whisking without stopping, drizzle in about ¼ of the hot milk.  Continue to whisk while slowly pouring in the remainder of the milk.  Bring the mixture to a boil while whisking and continue to whisk for 2 minutes at a boil.  Remove from the heat and whisk in the vanilla.  Let cool 5 minutes before whisking in the bits of butter until fully incorporated and the mixture is smooth.  Cover the surface of the custard with plastic wrap and refrigerate until cool.  Remove from the fridge and whisk again before scooping into tart shells, alternating with a layer of sliced banana until you reach the top of the shell.