As an adult, I haven't chased it too hard, and I never have beer in the house, though I have tried melted cheddar + mustard a few times. Still, I do like the flavor. Some years ago Trader Joe's had a month's special cheese that was "English ale cheddar with mustard", or so I have recorded in my diary. It tasted like rarebit. Alas it never re-appeared.
But I was shopping at Roche Bros last week, and found a cheese like it... or possibly the actual cheese, given how TJ rebrands things. Kilchurn Estate mustard & ale cheddar cheese. Tastes like I remember. No surviving price tag, so I can't tell you what it cost, but I'm charmed to know that I can have it again and again.
See the DW comments at https://mindstalk.dreamwidth.org/505461.html#comments