kosher salt and freshly ground black pepperto taste
In a medium bowl, whisk together mustard, egg yolk, beer and Worcestershire sauce. Season lightly with salt and freshly ground black pepper. Stir in shredded cheddar until well blended (the cheese should be uniformly wet with no liquid remaining on the bottom of the bowl.).
Arrange bread slices and tomato slices on a baking sheet. Drizzle tomato slices with olive oil and season with salt and pepper. Broil 3 minutes until bread is a light golden brown.
Remove from broiler and spread cheese mixture evenly over each bread slice, all the way to the edges. Broil until melted and bubbly, 3 to 4 minutes more.
Top of each bread slice with two broiled tomato slices on and serve immediately.