Pour the cream into a small saucepan, add the vanilla pod and seeds, and place over medium heat until hot and steamy, swirling the pan occasionally. Cover and let steep while you proceed with the recipe.
Meanwhile, pour the water into a medium-sized, heavy-bottomed saucepan. Add the corn syrup, then carefully pour the sugar into the center of the pan. If any sugar crystals stick to the sides of the pan, brush them down into the water with moistened fingers.
Cover the pot with a lid and, without disturbing the pan, cook over medium heat until the sugar is dissolved, about 3 minutes (the steam will wash down any wayward sugar crystals).
Remove the lid and continue to boil, without stirring, until the mixture turns a deep amber, gently tilting the pan to encourage even caramelization and brushing down the sides of the pan with a damp pastry brush if you see any sugar crystals forming on them. This will only take a few minutes; watch the pot carefully toward the end, and reduce the heat to low if you’re nervous.
When the mixture turns a dark amber (if the mixture is bubbly, you may need to place a drop of caramel on a white, heatproof plate to check), immediately swirl in the butter, then gently and slowly whisk in the cream. Return the pot to low heat and whisk gently to dissolve any hardened caramel that may be hanging out on the bottom or corners of the pan.
Strain the caramel into a heatproof bowl and let stand, stirring occasionally, until cooled and thickened slightly.
Cool the caramel to room temperature, or refrigerate until needed, up to 1 month.
Trifles:
In a medium bowl, toss together the peaches with the smaller amounts of sugar and lemon, adding more of either if you like. Let sit until juicy, at 15-30 minutes.
In the bowl of a stand mixer fitted with the paddle attachment, combine the cream, mascarpone, vanilla, and salt. Whip on medium-high until the mixture holds soft peaks. Cover and refrigerate until needed, up to 2 days.
Layer the ingredients into 8-ounce jars or cups as follows: crumbled gingersnaps, whipped mascarpone, caramel, peaches. Repeat each layer once more.
Serve right away, or cover and chill for up to a few hours. When ready to serve, drizzle with extra caramel and to with a sprinkle of gingersnap crumbles.
