Make the custard in advance. Heat the milk in a saucepan to a simmer, and then remove it from the heat.
In another saucepan, whisk together 3 of the eggs, with the maple syrup and the cornstarch. Slowly pour the hot milk in a thin stream into the eggs, whisking constantly to prevent scrambling the eggs.
Place the saucepan over low heat and whisk constantly until it thickens, about five minutes. Transfer the custard into a glass bowl, cover tightly, and refrigerate until completely cool.
To make the choux pastry: Combine the three flours in a bowl and set aside.
Pour the water and olive oil into a small saucepan and bring it to a boil. As soon as it boils add the flour mixture, stirring with a wooden spoon until it forms a ball on the spoon. Remove it from the heat and let it cool for five minutes.
Add the remaining two eggs, beating with an electric beater until smooth.
Heat the oven to 375 °F. Line a baking tray with a Silpat or baking paper. Scoop the dough onto the tray into 12 tablespoon-sized balls about two inches apart.
Place the pan in the oven and bake for about 25 minutes, until browned and puffed. Remove from the oven and allow them to cool completely.
Heat the chocolate chips in a bowl in the microwave for 15-second intervals until melted. Stir to make sure it is uniformly melted.
When cool, slice the choux in half. Scoop about 1 tbsp of custard into the puff, and cover with the top. Spoon the melted chocolate on the top of each puff. Serve immediately or refrigerate for up to 48 hours.