I am currently visiting my relatives in France, about 10 days ago I landed in Luxemburg, having some friends working there I met one of them for lunch. We went to the Beef Bar Junior, located in the shopping mall Auchan on the Kirchberg in Luxemburg City.
As its name suggests it, it’s specialised in beef. It’s not very big so be sure to book, it’s cosy and the staff is quite friendly. They have some lunch specials as well as à la carte menu. I went for one of their lunch specials and had the Beef-Grill plate: 450g of beef (3 pieces of black Angus) and corn fries. It also comes with a salad and a glass of wine (that I changed into water ^^). The service was quite quick and the beef was perfectly cooked, rare just I asked it. The meat is tender and full of taste, excellent. The corn fries are also quite nice.
As for the prices, it can seem expensive, but well worth the quality!