In a large bowl, whisk together the flour, cocoa powder, sugar, and salt.

In a separate bowl, whisk together the milk, eggs, melted butter, and vanilla extract.

Gradually add the wet ingredients to the dry ingredients, whisking constantly until smooth. Be careful not to overmix, as this can develop the gluten in the flour and make the crepes tough. A few small lumps are okay.

Cover the bowl and refrigerate the batter for at least 30 minutes. This allows the gluten to relax, resulting in more tender crepes. You can even refrigerate it overnight for even better results.

In a medium saucepan, combine the raspberries, sugar, and lemon juice.

Cook over medium heat, stirring occasionally, until the raspberries have softened and released their juices, about 5-7 minutes.

If you want a thicker filling, whisk the cornstarch with 1 tablespoon of cold water to form a slurry. Stir the slurry into the raspberry mixture and cook for another minute or two, until thickened.

Remove from heat and let cool slightly.

Heat a lightly oiled crepe pan or non-stick skillet over medium heat. The pan is ready when a drop of water sizzles and evaporates quickly.

Pour about 1/4 cup of crepe batter onto the hot pan, immediately tilting and swirling the pan to spread the batter into a thin, even circle.

Cook for about 1-2 minutes per side, or until the edges are lightly golden brown and the crepe is cooked through. Use a thin spatula to carefully flip the crepe.

Transfer the cooked crepe to a plate and repeat with the remaining batter, stacking the crepes on top of each other. You can keep them warm in a low oven (200°F) if desired.

For the chocolate sauce (optional): Place the chocolate chips, heavy cream, and butter in a microwave-safe bowl.

Microwave in 30-second intervals, stirring after each interval, until the chocolate is melted and smooth. Alternatively, you can melt the chocolate using a double boiler.

To assemble using the classic fold method: Lay a crepe flat on a plate, spoon a generous amount of raspberry filling onto one half of the crepe, fold the crepe in half, and then in half again, creating a quarter-circle shape, drizzle with chocolate sauce (if using) and garnish with powdered sugar and fresh raspberries.

To assemble using the rolled crepes method: Lay a crepe flat on a plate, spoon a line of raspberry filling down the center of the crepe, carefully roll the crepe up tightly, drizzle with chocolate sauce (if using) and garnish with powdered sugar and fresh raspberries.

To assemble using the crepe cake style: Lay a crepe flat on a plate, spread a thin layer of raspberry filling over the entire crepe, top with another crepe and repeat the process, layering the crepes and filling until you have used all the crepes, cut the crepe "cake" into wedges and serve, drizzle with chocolate sauce (if using) and garnish with powdered sugar and fresh raspberries.