Preheat the Oven to 250ºF (120ºC). Position the oven racks to the upper third and lower third positions. Line 2 large jelly roll pans with parchment paper. Set them aside.
Brown Butter: Melt the butter in a saucepan over medium heat. Once melted, continue heating the butter until it starts bubbling feverishly. Start stirring the butter frequently to keep it from burning. Gradually, the milk solids at the bottom and sides of the saucepan will start turning golden, like caramel. Reduce the heat slightly and continue stirring constantly to prevent burning. Right when the milk solids start turning into the color of medium to dark roast coffee beans, turn off the heat and add the maple syrup. Adding the maple syrup immediately will help keep the butter from browning further, as the solids can blacken and burn very quickly at this stage. It usually takes me about 2 to 3 minutes to brown the butter after it has melted (less time if you’re making a half batch).
Finish the Glaze: Add the soy sauce (or tamari), vanilla, and salt to the saucepan and whisk everything together. Remove the saucepan from heat.
Toss Snack Mix: Divide the corn Chex, pretzels, and nuts between 2 large bowls. Mix the contents in each bowl.
Add Glaze & Furikake: Divide the glaze between the two bowls. Use 2 spatulas to toss and coat the dry ingredients with the glaze. Then, sprinkle 1/4 cup of furikake into each bowl. Toss again to distribute the furikake.
Bake Chex Mix: Spread the furikake Chex mix over the lined baking pans. Bake for 1 hour, stirring halfway through baking. Make sure to also swap the position of the baking pans.
Let Chex Mix Cool: Remove the baking pans from the oven. Let the Chex mix cool for 5 to 10 minutes and give everything a stir to prevent clumping. You can sprinkle more furikake over the Chex mix, if you like. The Chex mix will turn crunchy as it cools.
Store Furikake Chex Mix in an airtight container at room temperature for 1 to 2 weeks, if it lasts that long.