Beat the butter, powdered sugar, and salt in the bowl of an electric mixer on medium speed for about 2 minutes, until smooth and creamy. Add the strawberries and beat for another minute, until combined. Transfer to a small bowl and chill in the refrigerator for at least 30 minutes, until firm.
Preheat the oven to 425°F and place a rack in the lowest part of the oven. Lightly grease a 12-cup mini popover pan.
Beat the flour, salt, milk, eggs, and melted butter in a medium bowl with a hand mixer, mixing until smooth. Divide the batter between 10 popover cups. Bake for about 15 minutes, until golden brown. Reduce the oven temperature to 350°F and bake for another 10 to 15 minutes, until cooked through but still doughy in the center. Serve warm with the strawberry butter.