In a small saucepot, combine the sugar with 1 cup of water. Stir often until the sugar dissolves and the mixture comes to a boil. Stop stirring and boil for 20-25 minutes until the liquid turns a rich amber color.
Heat the remaining 1 cup of water in a microwave-safe bowl for 60-75 seconds until hot, but not boiling. VERY CAREFULLY pour the water into the pot (stand aside, it WILL splatter!), then stir until the syrup turns a caramel hue. This will only take 2-3 minutes to achieve.
Move the pot off the heat and stir in the vanilla extract. Let cool 10 minutes or so on the counter. Leftover syrup will keep for up to 2 weeks in the fridge.
In a shaker, combine the caramel syrup with the tequila, Cointreau, and lemon juice. Fill with ice and shake until cold. Pour into a cocktail glass and top with sparkling apple cider. Garnish with apple slices!
Notes
*Caramel-dripped rim: Whip up a batch of my homemade caramel or melt 4 soft caramel candies in a shallow microwave-safe bowl for 10-15 seconds. Dip the rim of your cocktail glass into the softened caramel and swirl to coat, letting some drip down the side of the glass.