Roast Beef Sandwich Recipe with Slow Roasted Tomatoes

Close-up of a steak sandwich with fresh greens on a wooden board.

5 from 3 votes

Roast Beef Sandwich Recipe with Slow Roasted Tomatoes

Perfectly cooked rare roast beef shines in my take on the classic roast beef sandwich with juicy slow-roasted tomatoes and sweet sauteed onions.

Prep Time15

Cook Time20

Total Time35

Course: Lunch, Sandwich

Cuisine: American

Servings: Sandwich

Calories: 602kcal

Author: Kate O'Malley

Ingredients

½ small red onion thinly sliced.
½ teaspoon butter for cooking the onions. Butter for spreading on the sandwich is optional.
½ teaspoon olive oil
2 slices crusty sourdough or 1 small baguette substitute bread of your choice
1 teaspoon wholegrain mustard
4 oz rare roast beef. Thinly sliced. More or less, depending on your taste. (either leftover roast beef, pre-roasted or deli-bought slices)
⅓ cup watercress. you can substitute with arugula or baby spinach.
5-6 slow-roasted tomatoes cut in half and juice retained.

Instructions

Place the thinly sliced onion in a frying pan with a small dob of butter and a drizzle of olive oil. Cook on medium heat, stirring often, being careful to sweat the onions, not burn them. Cook until the onions are soft and caramelized.
Optional: As the onions soften, add a small drizzle of balsamic vinegar and continue to stir (the balsamic will help the onions become a nice, sweet, jam-like consistency).
Spread the whole grain mustard on one slice of the bread, layer with slices of roast beef and top with the caramelised onion.
Top with watercress and roasted tomato halves. Drizzle with any of the tomato juice before topping with the other slice of bread.

Notes

Recipe Variations

Salad Greens: Baby spinach or arugula are good options for a roast beef sandwich.
Mustard: You can use any mustard you prefer. Horseradish cream is also a good choice if you like some heat.
Cheese: I don’t add cheese to this sandwich because I don’t feel it needs it. If you want to add cheese, cheddar, provolone, Swiss, and blue cheese are all good options.

Tips

Thin Slices of Beef: Thin slices are key for a tender sandwich that won’t fall apart when you bite into it. If you have an electric slicer, use it for uniform, thin slices. Otherwise, let the roast beef chill in the refrigerator before slicing it with a sharp knife, as cold beef is easier to slice thinly.

Nutrition