In a small saute pan, set over medium-low heat, melt 1 tablespoon of butter. Add the leeks and a few pinches of salt. Cook slowly, stirring regularly, until softened, about 7 to 10 minutes.

To a medium saucepan, set over medium heat, melt the remaining 2 tablespoons butter. When melted, stir in the all-purpose flour and cook for about 1 minute. Pour in the milk and whisk until combined and thickened, about 1 minute. Pour in the beer and again give it a good whisk. Cook the sauce for an additional minute or so. During this time it will thicken slightly. Mix in the Dijon mustard, pinch of crushed red pepper, Worcestershire, shredded cheese and egg yolk; stir until cheese has melted. Give it a taste and adjust the salt to your liking. I added about 1/2 teaspoon of salt.

Divide the melted leeks among the slices of toasted bread. Top with a few spoonfuls of the welsh rarebit and garnish with a sprinkling of Italian parsley.