- 1 1/4 cups pure maple syrup (amber or Grade B)
- 3/4 cup heavy cream
- 2 teaspoons cider vinegar
- Pinch of salt
- 3/4 stick (6 tablespoons) unsalted butter, softened
- 1/3 cup sugar
- 1 large egg
- 1/2 teaspoon vanilla
- 1 cup cake flour (not self-rising)
- 1 teaspoon baking powder
- 1/4 teaspoon salt
- Special equipment: an 8-inch square glass baking dish (2 inches deep)
- Put oven rack in upper third of oven and preheat oven to 350°F.
- Stir together maple syrup, heavy cream, cider vinegar, and pinch of salt in a small saucepan and bring to a boil, then remove from heat.
- Beat together butter and sugar in a bowl with an electric mixer until light and fluffy, about 1 minute. Add egg and vanilla, then beat until just combined (batter will be very thick).
- Sift flour, baking powder, and salt together into egg mixture and stir with a rubber spatula until just combined.
- Pour 1/3 cup syrup mixture into baking dish. Divide batter in bowl into 6 mounds with rubber spatula and spoon each mound onto syrup mixture in baking dish, spacing mounds evenly. Pour remaining syrup mixture over and around mounds.
- Bake until topping is golden and firm to the touch, 25 to 30 minutes. Serve warm, with crème fraîche or sour cream if desired.