1. Position a rack in the lower third of the oven and preheat it to 450°F (232°C). This high temperature is crucial for achieving that initial pop in the popovers.
2. Place 1 teaspoon of butter in each cup of a standard 12-cup muffin pan. Transfer the pan to the oven for 3 to 5 minutes, allowing the butter to melt and the pan to heat up. You want the pan screaming hot to help the popovers rise beautifully.
3. In a medium bowl, vigorously whisk together the milk and eggs until frothy, about 1 minute. This aeration is key! Add 1 tablespoon melted butter, vanilla, flour, and salt. Whisk until combined. It's perfectly fine if there are small lumps in the batter; they will work themselves out during baking.
4. Carefully remove the pan from the oven, and swirl the melted butter around the cups to grease them well. Then evenly divide the batter among the popover cups, filling them about 3/4 full. This gives them room to puff up!
5. Transfer the pan to the oven and bake for 15 to 18 minutes, until they are puffed, golden, and crisp. Resist the urge to open the oven door during baking, as this can lead to deflation.
6. To make the brown butter, add 4 tablespoons of butter to a skillet set over medium heat. Allow the butter to brown, swirling it occasionally, until it smells toasted and is a deep golden color, about 3 to 4 minutes. Remove it from the heat and set aside.
7. In a shallow bowl, combine granulated sugar, lemon zest, and vanilla powder. This mixture adds a lovely citrusy sweetness to the popovers.
8. For the strawberries, toss the sliced strawberries with granulated sugar and the optional St. Germain. Let them sit for 5 to 10 minutes. This resting time will allow them to release their juices and create a delicious topping.
9. Once the popovers are done baking, brush each warm one with the brown butter, then roll them through the lemon-sugar mixture. Finally, smear each popover with butter and top with the strawberries. Enjoy them warm for the best experience!
