Melt the butter in a heavy-based medium saucepan. Add the brown sugar and cook until dissolved, stirring occasionally, 2 to 3 minutes. Add the cream, bring to a simmer, stirring, and cook until you have a nice thick butterscotch sauce.
Meanwhile, combine the corn flour and salt in a bowl. Whisk in a couple tablespoons of the milk until smooth, then whisk the mixture into the remaining milk in a large bowl.
Whisk in the egg yolks and vanilla and then gradually add the hot butterscotch sauce, whisking constantly. Wipe out the saucepan and strain the mixture through a fine-mesh sieve back into the pan. Cook over medium heat, stirring regularly, until the custard starts to thicken, 5 to 6 minutes. Remove from the heat and stir in the vodka.
Pour into pretty glasses or ramekins and chill for at least 1 hour and up to 3 days.
Serve garnished with honeycomb.
For a lighter result, chill the custard in a bowl with plastic pressed to the surface to prevent a skin from forming. When ready to serve, whip the pudding lightly with a whisk or in stand mixer with the paddle attachment before spooning it into glasses or ramekins.