Preheat the oven to 200°F and place an oven-safe plate or baking sheet inside to keep cooked crepes warm.

In a medium bowl, whisk together the 3/4 cup all-purpose flour and 1/4 cup granulated sugar, breaking up any clumps.

In a separate large bowl, whisk the 3 large eggs, 1 1/4 cups milk, 6 tablespoons of the melted butter (reserve the remaining 2 tablespoons of the melted butter), and 1/4 teaspoon vanilla extract until smooth.

Add the flour mixture to the wet ingredients in several additions, stirring gently to incorporate after each addition. Do not overmix. (Optional: refrigerate the batter for 1 hour or up to overnight.)

Heat a crepe pan or nonstick frying pan over medium heat. Brush the pan bottom lightly with the reserved 2 tablespoons melted butter.

When the butter is bubbling, add 3 tablespoons of batter to the center of the pan. Immediately tilt and swirl the pan so the batter spreads into a thin layer.

Cook the crepe about 1 minute, until the bottom is lightly browned, then flip (using two spatulas if helpful) and cook about 1 more minute. Transfer the cooked crepe to the oven-safe plate in the preheated oven, stack, and cover with a clean towel while you cook the remaining crepes.

While the last crepes cook (or after finishing them), prepare the Salted Lemon Butter Caramel: juice 2 of the lemons and set the juice aside. Slice the remaining 2 lemons into 1/4" thick rounds.

Heat a frying pan over medium-high heat and add the 4 tablespoons butter. When the butter begins to bubble, add the 1/3 cup brown sugar and the generous pinch of sea salt; whisk until the sugar is incorporated and the mixture is smooth.

Add the lemon slices to the pan and cook about 2 minutes per side, then pour in the reserved lemon juice and let the mixture simmer for about 2 minutes more until slightly thickened.

Spoon the salted lemon butter caramel and lemon slices over folded crepes. Garnish with fresh mint or thyme and serve immediately.