Step 1

Place a 9 by 5-inch loaf pan in the freezer.

Step 2

Coarsely chop 4 ounces white chocolate if using and place in a medium bowl (or measure out 1/2 cup white chocolate chips. Add 1/2 teaspoon ube extract and a pinch of kosher salt.

Step 3

Heat 1/4 cup plus 1 tablespoon heavy cream in a small saucepan over medium-high heat until bubbling around the edges, about 2 minutes. Immediately pour over the white chocolate. Let sit for 1 minute, then stir until the white chocolate is melted and the mixture is smooth. Let cool for 15 minutes.

Step 4

Place 1 (14-ounce) can sweetened condensed milk, 2 teaspoons vanilla extract, and 1/8 teaspoon kosher salt in a large bowl and whisk until combined.

Step 5

Pour 2 cups cold heavy cream into the bowl of a stand mixer (or large bowl if using an electric hand mixer or whisking by hand). Beat with the whisk attachment on medium-high speed until stiff peaks form, 2 to 3 minutes.

Step 6

Transfer about 1 cup of the whipped cream into the sweetened condensed milk mixture and stir to combine with a flexible spatula. (This lightens the condensed milk and makes it easier to fold in the rest of the whipped cream.)

Step 7

Add the remaining whipped cream and gently fold together. It will initially look very lumpy, but as you continue to fold, the mixture will smooth out and become soft and silky. Stop when you see just a few small lumps here and there — be careful not to deflate the mixture too much or over-mix.

Step 8

Using the spatula, transfer about 1/3 of the ice cream base into the loaf pan and smooth the top. Drizzle about 1/3 of the ube ganache over the top. Repeat layering half of the remaining ice cream base and half of the remaining ube ganache. Layer the remaining ice cream base and ube ganache. Use a knife to swirl the ube ganache into the ice cream base.

Step 9

Cover the pan tightly with plastic wrap. Freeze until solid, at least 6 hours and up to 1 week.