In a large bowl, whisk melted butter with brown sugar and granulated sugar until glossy.

Add egg yolks and vanilla; whisk until smooth.

In another bowl, mix flour, cocoa powder, and salt. Sift dry mix into wet; stir gently until smooth.

Warm milk and cream in a saucepan until small bubbles form (do not boil).

Slowly whisk ⅓ of warm liquid into the batter to temper the eggs.

Pour the tempered batter into the saucepan with remaining liquid. Cook over medium-low heat, stirring constantly, until thick enough to coat the back of a spoon.

Strain the base through a fine mesh sieve into a clean bowl. Cool completely, then chill 4+ hours or overnight.

Churn in an ice cream maker until soft-serve texture.

Gently fold in chilled brownie chunks and fudge swirl.

Freeze 2+ hours before serving.