Remove pan from heat and whisk in sweetened condensed milk and butter (mixture will bubble vigorously) until smooth. Fit pan with thermometer and return to medium-low heat. Cook, whisking constantly, until thermometer registers 240°. Remove from heat and whisk in walnut liquor, cinnamon, kosher salt, and dried banana chips (reserving a few teaspoons for the top). Pour into prepared pan; let cool. Sprinkle caramel with chopped walnuts, reserved banana chips, and lava salt, cut into ¾” pieces, and wrap individually in waxed paper.