Preheat your oven to 350°F and line a 9x13-inch pan with parchment paper for easy removal and cleanup.

In a large saucepan, combine the maple syrup, brown sugar, and chopped nuts (if using). Bring the mixture to a gentle boil over medium to medium-high heat. Once boiling, reduce the heat to medium-low and let it simmer for another 5 minutes, stirring occasionally to keep it from sticking.

Take the saucepan off the heat and stir in the salt and butter until completely melted and smooth. Set the mixture aside to cool slightly while you prep the crust.

In a medium bowl, mix together the flour and brown sugar. Add in the butter and stir until the mixture becomes crumbly. Press this evenly into the bottom of your prepared pan to form the crust.

Bake the crust for 10 minutes, then remove it from the oven and set it aside.

In a small bowl, whisk together the eggs and flour. Slowly stir this into the cooled maple syrup mixture until well combined. Pour the filling over the pre-baked crust and smooth it out evenly.

Return the pan to the oven and bake for another 25 to 30 minutes, or until the top looks mostly set.

Allow the bars to cool completely at room temperature, then transfer to the fridge to chill before slicing.