In a small sauce pan, melt the butter over medium heat. When melted, stir in the flour and cook for 1-2 minutes, until completely smooth and incorporated. Whisk together the IPA, milk, and dijon in a liquid measuring cup and slowly incorporate in a thin stream, whisking constantly. Whisk occasionally until the sauce thickens and comes to a gentle simmer. Stir in the cheese until melted and then remove from the heat and whisk in the egg yolk. Taste and season. Pour or spread onto lightly buttered toast of choice. Enjoy immediately!
Notes: We only had IPA in the fridge so we used that – traditionally porter or ale is used. We liked the slight bitterness that the IPA brought to the party. Also, classically dry mustard is used, as well as a bit of Worcestershire. If, like us, you aren’t going to finish all the sauce, pop it in the fridge and later on, when you’re hungry, either heat it up over low heat or spread it on toast and then broil it for extra delicious rarebit!