Pour the whole milk into your blender first, then add the strawberry syrup or puree and vanilla extract. Stir the mixture with a spoon or blend on low speed for 5-10 seconds until the strawberry syrup is evenly distributed throughout the milk, creating a uniform pink color with no streaks.
Add the softened vanilla ice cream to the blender, breaking it into 2-3 chunks with a spoon before adding to help it blend more smoothly. If using fresh strawberries instead of frozen, add 2-3 ice cubes at this point to ensure the shake is properly chilled and thick.
Add the fresh or frozen strawberries and a pinch of salt to the blender. The salt may seem unusual, but it's essential for replicating McDonald's flavor profile—it enhances the sweetness and adds depth to the strawberry taste.
Blend on medium speed for 30-45 seconds, until the mixture is completely smooth and creamy with no visible strawberry chunks or ice crystals. Stop and scrape down the sides of the blender with a spatula if needed, then blend for another 10-15 seconds to ensure everything is fully incorporated.
Check the consistency by tilting the blender pitcher—the shake should flow slowly like soft-serve ice cream, not too thick and not too thin. If it's too thick, add 2-3 tablespoons of milk and blend for 5 more seconds; if too thin, add a small scoop of ice cream and blend briefly.
Pour the shake into a tall glass, filling it about three-quarters full. The shake should be thick enough to require a spoon or thick straw to drink, mimicking McDonald's signature texture.
Top with whipped cream if desired, then drizzle with 1 teaspoon of strawberry syrup in a thin stream across the top for an authentic McDonald's presentation. This adds visual appeal and an extra burst of strawberry flavor on the first sip.
Serve immediately with a thick straw or spoon, as the shake will begin to melt within 5-10 minutes. For the best experience, drink within 10-15 minutes while it maintains that perfect creamy, cold texture that McDonald's shakes are known for.