Preheat your oven grill to a medium to high setting. Place the bread slices on a baking tray and lightly toast them on both sides until golden. Set aside while you prepare the cheese mixture.

In a medium saucepan, melt the butter gently over low heat. Sprinkle in the flour and whisk steadily for 1 to 2 minutes until a smooth paste forms. This helps cook out the raw flour taste.

Gradually pour in the ale while whisking continuously. Keep the mixture smooth and free of lumps. Allow it to simmer for 2 to 3 minutes until slightly thickened, resembling a thin sauce.

Lower the heat and add the grated Cheddar a handful at a time. Stir slowly until the cheese melts into a glossy, thick mixture. Avoid boiling, as overheating can cause the cheese to separate.

Stir in the mustard, Worcestershire sauce, and a good grind of black pepper. Taste at this stage and adjust seasoning if needed, keeping in mind the strong character of the Cheddar and ale.

Remove the pan from the heat and allow the mixture to cool slightly for a minute. Whisk in the egg yolks one at a time until well combined. This enriches the sauce and adds body.

Lay the toasted bread slices on the baking tray again. Spoon the cheese mixture generously over each slice, spreading it evenly to the edges to prevent burning.

Slide the tray under the preheated grill. Cook for 3 to 5 minutes until the topping is bubbling and the surface develops a golden, slightly crisp finish. Keep a close eye to avoid scorching.

Transfer the Welsh Rarebit slices to warm plates. Serve immediately, perhaps with a crisp salad or pickles on the side. The balance of richness and tang is best enjoyed hot.