Make the chocolate French toast batter
In a bowl, combine the melted butter, cocoa powder, and espresso powder until smooth.
Add the eggs and sugar and whisk until combined. Slowly whisk in the half and half until the mixture is smooth and evenly blended.
Soak the bread
Dip each slice of bread into the chocolate custard, coating both sides.
Place the dipped bread on a plate or baking sheet and allow it to rest for 10 minutes so the custard can absorb into the bread.
Fill with chocolate
Place 2 to 3 ounces of chocolate chips in the center of each slice.
Gently press around the edges of the bread to help seal the chocolate inside and create the lava center.
Cook the French toast
Preheat the oven to 300°F.
Lightly butter a cast iron skillet and heat over medium-low heat.
Cook the French toast for about 3 minutes on each side, or until the exterior is browned and cooked through.
Finish in the oven
Transfer the French toast to the preheated oven and bake for about 20 minutes, or until the chocolate chips inside are completely melted.
Serve
Serve warm with butter, a drizzle of olive oil, and flaky sea salt.
Cut into the center while warm for the full chocolate lava effect.