For the creme anglaise: Bring the milk, cream, vanilla and salt to a simmer in a medium saucepan over medium heat. Whisk the egg yolks and sugar in a medium heatproof bowl until well combined.
When the milk mixture comes to a simmer, pour about a quarter of it into the yolk mixture while whisking constantly to combine. Place the saucepan with the remaining milk mixture over low heat. While whisking constantly, add the yolk mixture to the saucepan. Whisk until the mixture begins to thicken, 1 to 2 minutes.
Switch to a silicone spatula and continue to cook over medium-low heat, stirring constantly, until the mixture is thick enough to heavily coat the spatula, 3 to 5 minutes. Remove from the heat, cover the saucepan and set aside.
For the waffles: Whisk together the flour, cocoa powder, sugar, baking powder and salt in a large bowl to combine. Whisk the buttermilk, oil and melted butter in a medium bowl until well combined.
Whip the egg whites in the bowl of a stand mixer fitted with the whisk attachment (or in a medium bowl with a handheld mixer) to medium peaks.
Add the buttermilk mixture to the flour mixture and whisk well to combine. Add about a quarter of the whipped egg whites and whisk more vigorously to combine. Add the remaining egg whites in 2 to 3 additions, folding gently after each addition until just incorporated. Gently fold in the mini chocolate chips.
Preheat a Belgian-style waffle iron to medium and grease as needed with nonstick spray. Scoop the waffle batter into the heated waffle iron, close and cook according to the manufacturer's instructions until the waffle is crisp, 4 to 5 minutes. Transfer to a wire rack. Repeat with the remaining batter.
Reheat the creme anglaise over low heat. Stir gently until fluid and warm, then gently strain into a serving bowl.
To serve, cut the waffles into quarters and serve alongside the creme anglaise for dipping. Or plate the waffles and allow guests to drizzle the sauce over their own waffles. Serve immediately.