Add the bitters and simple syrup into a serving glass. Stir. Place the ice into the glass and pour the whiskey over the ice. Stir, add the orange slice and serve chilled.

for the rose simple syrup: Place 1 cup sugar, 1 cup water and 1/2 teaspoon rose water into a small saucepan. Heat over low heat until the sugar is dissolved, about 10 minutes. Remove from the heat and let cool. Pour the syrup into an airtight container and store in the fridge. Use as directed.