Line a baking sheet with parchment so the bark releases cleanly.

Toast pistachios and almonds in a dry skillet until they smell nutty and look a shade darker. Pull them before they turn deep brown.

Melt butter in a saucepan over medium heat until fully liquid, no sizzling or browning.

Stir in sugar, maple syrup, salt, and cardamom until smooth and glossy.

Cook until the color shifts from pale to deep golden and the bubbles look thicker and slower. If it darkens fast, lower the heat.

Off heat, stir in vanilla and baking soda. It should foam up quickly and look lighter.

Fold in toasted nuts and 2 tablespoon rose petals while the mixture is still fluid. Pour onto the lined sheet and spread to an even layer before it starts setting.

Sprinkle crushed pistachios, remaining rose petals, and flaky sea salt while the surface is still tacky so it sticks.

Cool at room temperature until firm, then chill to fully harden. Use a sharp knife dipped in hot water and wiped dry between cuts for cleaner edges.