Grease a square 9-inch baking pan with 2 teaspoons butter.
Combine sugar and water in a large saucepan over medium heat. Cook and stir until sugar dissolves. Pour in sweetened condensed milk; cook and stir until mixture starts to bubble, about 5 minutes. Reduce heat to low. Add cashews; cook, stirring frequently, until mixture thickens, about 10 minutes.
Stir 2 tablespoons butter, vanilla extract, and rose extract into the mixture. Continue to cook, stirring frequently, until mixture is very stiff, 8 to 10 minutes. Pour into the buttered baking pan. Spread flat using a spatula or the back of a spoon.
Cool toffee until firm, about 15 minutes. Cut into 1-inch pieces and transfer to an airtight container.