Preheat the oven to 450°F (230°C). Adjust the oven rack to the lowest position.sss
Place the milk in a bowl and microwave on high for 1 1/2 to 2 minutes, or until warm to the touch.
In a large bowl, sift together the flour, salt, and baking powder.
Crack the eggs into the bowl of a stand mixer fitted with a whisk and beat on medium speed until foamy and pale in color, about 3 minutes.
Turn down the mixer to low and add the warm milk. Gradually add the flour mixture, increase the speed to medium or medium-high, and beat for about 2 minutes.
Turn the machine off and let the batter rest for 1 hour at room temperature.
Spray a popover tin generously with nonstick spray. Fill the popover cups almost to the top with the batter and place the popover tin on a rimmed baking sheet. If you only have a single popover tin, you'll need to bake them in 2 batches.
Bake for 15 minutes. Turn down the oven temperature to 375°F and bake for 30 to 35 minutes more, until the popovers are golden brown on the outside and airy on the inside.
Turn out the popovers and serve hot, with strawberry butter if desired. To reheat any leftover popovers without compromising texture, warm them in a preheated 400°F oven for about 3 1/2 minutes.