Toss the sliced strawberries with 2 tablespoons of the sugar and let sit at room temperature for 20 minutes, until they slump and release their juices.

Blend the berries and all accumulated juice until smooth. Press through a fine-mesh sieve, discarding seeds and pulp. You should have about 1 cup of strained purée.

In a large pitcher, whisk the remaining sugar and the salt into about half the milk until fully dissolved and no grit remains, about 1 minute.

Whisk in the remaining milk, heavy cream, strawberry purée, vanilla, and freeze-dried strawberry powder if using. Keep the mixture cold.

With the auger and drip tray seated in the Ninja Slushi, pour the base in through the top opening, keeping it between the MIN and MAX fill lines. Lock the lid.

Select the MILKSHAKE preset and start the machine. Let it run 35 to 50 minutes.

The milkshake is ready when the mixture climbs the auger and holds a soft ripple instead of falling flat. Place a glass under the spout and pull the handle to dispense.

Serve immediately with a wide straw. Rinse the vessel right away with warm water using the rinse cycle.