In a small saucepan over medium, combine ½ cup water, the maple syrup, vinegar, 4 tablespoons of whiskey, 2 tablespoons of butter and ¼ teaspoon of salt. Bring to a boil, stirring occasionally. Reduce to low and simmer for 5 minutes. Remove from the heat and set aside.

In another small saucepan over medium, melt the remaining 6 tablespoons butter. Cook, swirling the pan, until the mild solids at the bottom are deep golden brown and the butter has the aroma of toasted nuts, about 5 minutes. Transfer to a medium bowl and cool to room temperature.

Meanwhile, heat the oven to 325°F with a rack in the middle position. Mist four 6-ounce ramekins with cooking spray and place on a rimmed baking sheet.

When the butter is cool, whisk in the sugar, milk, egg, vanilla and remaining 2 tablespoons whiskey. Set aside.

In a food processor, process the pecans until finely ground and beginning to clump, 30 to 40 seconds. Add the flour, baking powder and ½ teaspoon salt, then pulse until combined, about 5 pulses. Add the butter mixture and pulse until a smooth, thick batter forms, about 5 pulses, scraping down the bowl once.

Divide the batter among the prepared ramekins. Gently pour the maple mixture over the batter in each ramekin. Do not stir. Bake until the cakes are puffed and the centers jiggle only slightly, 25 to 30 minutes. Let cool on the baking sheet for 10 minutes before serving; the cakes will fall slightly as they cool.