Brew a strong cup of coffee using your preferred method, making it slightly stronger than you normally would since the ice will dilute it. Allow the coffee to cool to room temperature for about 15-20 minutes, or refrigerate it for faster cooling until it's no longer hot to the touch.
Fill a tall 16-ounce glass with ice cubes, filling it about three-quarters full to ensure your drink stays cold and refreshing. The ice should reach near the top of the glass, leaving just enough room for the liquid ingredients.
Pour the cooled coffee over the ice, filling the glass about two-thirds full. You should hear a pleasant crackling sound as the coffee hits the ice, and you'll see the ice begin to glisten with the dark coffee coating.
Add the vanilla syrup to the coffee, measuring carefully to achieve that signature McDonald's sweetness. The syrup will initially sink to the bottom of the glass, creating a darker layer that you'll mix in the next step.
Pour in the half-and-half, watching as it swirls through the coffee creating beautiful marbled patterns. The cream will naturally begin to lighten the coffee to that recognizable caramel color.
If using a cocktail shaker or mason jar, transfer the mixture and shake vigorously for 10-15 seconds until everything is thoroughly combined and slightly frothy on top. Alternatively, stir well with a long spoon for about 30 seconds until the color is uniform throughout.
Taste your iced coffee and adjust sweetness if needed by adding the optional tablespoon of sugar, stirring until it completely dissolves. The sugar should disappear within 20-30 seconds of stirring, leaving no grittiness.
Pour the finished iced coffee back into your serving glass if you used a shaker, and add a straw for sipping. Serve immediately while the drink is ice-cold and enjoy your homemade McCafe-style iced coffee that tastes just like the original.