Line an 8×8-in (20×20-cm) pan with parchment paper.
In a large saucepan on low-medium heat, combine macadamia butter, syrup, sugar, salt, agar powder, and vanilla.
Stir continually as mixture heats until agar powder is fully dissolved (reduce heat if mixture starts bubbling).
Remove from heat and stir in cereal, making sure to fully incorporate with nut butter mixture.
Transfer mixture to pan and press in evenly (use an edge of parchment paper to press without sticking).
Refrigerate to cool completely, then cut into squares.
Makes 16 squares.