Line a large baking sheet with parchment paper, letting it hang over the edges for easy removal later.
Reserve 4 oz of the chopped white chocolate. Place the remaining 8 oz in a heatproof bowl set over a pot of barely simmering water, making sure the bowl doesn't touch the water. Stir gently until melted and smooth, about 3-4 minutes.
Remove the bowl from heat and immediately stir in the reserved 4 oz of chocolate until completely melted and the temperature drops slightly. This simple tempering technique helps the bark set with a glossy finish and clean snap.
If using rose water, stir it in now along with half of the crushed strawberries, folding gently to distribute.
Pour the chocolate onto the prepared baking sheet and use an offset spatula to spread it into a rough rectangle about 1/4-inch thick. Work quickly before it starts to set.
Immediately sprinkle the remaining strawberries and all the rose petals over the surface, pressing them gently into the chocolate with your fingertips. Finish with a light sprinkle of flaky sea salt.
Refrigerate for 15-20 minutes until completely firm and no longer tacky to the touch.
Lift the bark out using the parchment overhang and break into irregular shards by hand or cut into squares with a sharp knife. Store in an airtight container with parchment between layers.