Line an 8 x 8" square pan with a sling of parchment paper.
In a large saucepan, bring the maple and rice syrups to a rolling boil for 1 minute, stirring frequently with a heat-proof spatula or wooden spoon (be careful not to let it boil over).
Remove from the heat and stir in the nut butter, ½ cup chocolate, 2 Tbsp coconut oil, and ¼ tsp fine-grain sea salt until everything is smooth and the chocolate is melted.
Fold in the rice cereal and pack the mixture firmly and evenly into the lined pan
In a small saucepan (or the same big one, if you've scraped it clean), melt the remaining ½ cup of chocolate and 2 Tbsp coconut oil together over very low heat, stirring constantly just until melted (be careful not to scorch the chocolate).
Pour the chocolate mixture over the rice mixture, spreading it smooth.
Sprinkle the nuts and flaky salt over the top.
Let the bars set at cool room temperature (about 2 hours) or in the refrigerator (about 1 hour) until firm.
Lift the sling out of the pan, trim away the edges if you like, and cut into 16 squares.
These treats are best the day they are made. They will keep at room temperature for several days, though the cereal will soften slightly.