Butter three 6-inch cake pans and line the bottoms with parchment. Preheat the oven to 350° F.
Sift the flour, soda, baking powder, and salt together and set aside.
Place chocolate and cocoa powder in a medium bowl.
Steep the dried roses in the boiling water for 5-7 minutes, then strain into the chocolate bowl. Whisk until combined and smooth; add rosewater.
In the bowl of a stand mixer with the paddle attachment, cream the butter and brown sugar until fluffy, 2-3 minutes. Add eggs, one at a time, scraping sides down with a spatula in between. Mix until well combined. Add sour cream and vanilla and mix.
Add about 1/3 of flour mixture into butter mix and gently combine. While mixer is running, pour half of the chocolate mixture in. Repeat alternating the flour and chocolate mixtures, ending with the last 1/3 of the flour mix.
Divide batter between the prepared cake pans and smooth out. Bake until set and just done, about 30-35 minutes. Allow to cool completely.