In a medium saucepan, whisk together the granulated sugar, cornstarch, and kosher salt.

Add in the milk, water, and lemon juice, then whisk until combined.

Add in the sliced frozen strawberries and cook over medium heat, stirring frequently and mashing the strawberries with the back of a spoon.

Cook until the mixture begins to bubble and thickens to a pudding-like consistency, about 4 to 6 minutes.

Once bubbling, continue to cook for an additional 30 seconds.

Remove from heat, then whisk in the butter.

Place a mesh colander over a heat-proof bowl and pour the curd through the colander to strain it, avoiding pressing down on the strawberries too hard.

After straining, whisk the curd until silky smooth, and let it sit at room temperature for about 30 minutes, then chill in the fridge for at least 30 minutes to an hour or until thickened.