Place chocolate and heavy cream in a medium bowl. Heat in the microwave for 45-60 seconds, or until it begins to boil. Remove from the microwave and stir until smooth. If still lumpy, return to the microwave for another 15 seconds, remove and stir until smooth.

Place Cocoa Puffs in a gallon ziploc bag, seal, then crush with a rolling pin. Transfer to a shallow dish.

Place a wire rack onto a rimmed baking sheet. Slice the croissants in half.

In a shallow dish, whisk together the egg yolks, hot chocolate powder, flour, salt, vanilla, and milk until blended.

Soak the croissants in the milk mixture until saturated but not falling apart, about 10 seconds per side. Pick up the croissant slice and allow excess mixture to drip off. Transfer to the crushed Cocoa Puffs, gently press coating onto croissant, flip over, and repeat with the other side. Place coated croissant onto another baking sheet; repeat with the remaining croissants.

In a skillet, heat 1 Tablespoon of oil and 1 Tablespoon of butter over medium heat. Once hot enough, transfer four croissant slices to the skillet and cook until golden brown, 1 to 3 minutes per side. Transfer to the baking sheet with the wire rack*, wipe the skillet with a paper towel, and repeat cooking with the remaining croissants, adding 1 Tablespoon more oil and butter for the last batch. Serve french toast warm with white chocolate ganache.