Cut the beef into bite-sized pieces and season with salt and pepper, rubbing it in.

Slice the onion, olives, and mushrooms thinly.

Heat olive oil in a pan over medium heat and cook the beef until its color changes.

Add the onion, mushrooms, and olives to the pan. Cook until softened, season with salt and pepper, and let cool.

Mix the egg, milk, cream, salt, and pepper in a bowl to create the egg mixture.

Brush melted butter onto a tart mold. Roll out the pastry sheet thinly and fit it into the mold. Trim excess pastry and press onto the sides.