Line a baking sheet with foil. In a medium skillet, stir the remaining 1/4 tsp. cinnamon and a large pinch of cayenne over medium-high heat until toasted and aromatic, about 1 minute. Add the sugar, remaining 1/8 tsp. salt, and 2 tbsp. of water. When the mixture starts to bubble, add the nuts and cook, stirring often, until caramelized and no liquid remains, 3 to 4 minutes. Pour mixture onto the foil, separating the nuts before the candy sets. Cool until hardened, about 15 minutes. Arrange nuts on top of tart or chop and scatter on top.