Place the sugar in a small saucepan over medium-high heat and whisk constantly until it fully melts into a deep amber syrup, about 3 to 5 minutes.

Add the butter to the melted sugar and whisk until smooth.

Lower the heat to a gentle simmer, then slowly pour in the heavy cream while stirring until the caramel is well blended.

Remove the caramel from the heat and let it cool completely.

Spread walnuts on a small baking sheet and bake at 350°F (177°C) for about 7 minutes, until lightly golden and fragrant.

Melt 2 tablespoons salted butter in a small saucepan over medium heat, stirring until it turns deep golden, about 2 to 5 minutes.

In a medium bowl, whisk together the sweetened condensed milk, vanilla, browned butter, and half-and-half until smooth.

In a separate bowl, whip the heavy cream with a hand mixer or stand mixer until stiff peaks form.

Gently fold the condensed milk mixture into the whipped cream until smooth and evenly combined.

Fold in the cooled toasted walnuts.

Spread half of the ice cream base into an 8 x 8-inch pan or a similar freezer-safe container.

Spoon half of the cooled caramel over the top and add the remaining ice cream base.

Drizzle the rest of the caramel and use a knife or fork to swirl the caramel lightly through the mixture.

Freeze uncovered for 3 to 5 hours, or until firm. Cover leftovers with foil or plastic wrap and keep frozen for up to 3 weeks.