Step 1

Split 1 vanilla bean down its length with a paring knife. Working with one half at a time, hold down the tip of the bean against the cutting board. Use the dull side of your paring knife — not the sharp side — and scrape the vanilla beans from the pod. Move from the tip of the pod, where you are holding it, and scrape down the entire length. Place the seeds and vanilla pod in a large pot.

Step 2

Finely grate the zest of 1 medium lemon in the pot. Juice the lemon; add 2 tablespoons to the pot and reserve 2 teaspoons for the raspberry sauce. Add 6 cups water and 1 1/2 cups granulated sugar to the pot. Bring to a boil over medium-high heat, stirring occasionally, until the sugar dissolves. Meanwhile, score an X on the bottom of 6 peaches with a paring knife.

Step 3

Lower the peaches into the boiling syrup and reduce the heat to maintain a simmer. Simmer for 10 minutes. Meanwhile, fill a large bowl halfway with ice and cold water.

Step 4

Turn off the heat. Using a slotted spoon, transfer the peaches to the ice water bath and let sit until cool to the touch, about 5 minutes. Remove the peaches from the water, peel, and discard the skin. Return the peaches to the poaching liquid and weight them down with a plate or bowl. Let sit for at least 2 hours, or let cool in the poaching liquid and refrigerate in an airtight container for up to 3 days. Meanwhile, make the raspberry sauce.

Step 5

Place the reserved 2 teaspoons lemon juice, 12 ounces frozen raspberries, 1/2 cup water, and 1/3 cup granulated sugar in a medium saucepan. Bring to a simmer over medium heat, stirring occasionally, until the sugar is dissolved and the raspberries have broken down, about 10 minutes total.

Step 6

Pour the mixture through a fine-mesh strainer set over a bowl. Press down on the solids in the strainer with a spatula to release any extra syrup from the raspberry pulp, and scrape on the underside of the strainer. Discard the contents of the strainer. Let the sauce cool before serving.

Step 7

When ready to serve, remove the peaches from the syrup. Pit and quarter the peaches. For each serving, top 4 peach pieces with vanilla ice cream and drizzle with about 2 tablespoons of the raspberry sauce.