Which of the following is a classic sauce made from stock, butter, and flour?

Velouté is indeed a classic sauce made from a thickened stock, butter, and flour. It serves as one of the foundational sauces in classical French cuisine and is considered a mother sauce. The process involves making a roux by cooking equal parts butter and flour together, and then gradually whisking in the stock to create a smooth sauce. This technique allows for a flavorful and versatile base that can be used to create many derivative sauces by adding various flavorings or additional ingredients.

In contrast, Hollandaise, Alfredo, and Béarnaise have different primary components and preparation methods. Hollandaise is an emulsified sauce made from egg yolks, butter, and lemon juice. Alfredo is a creamy sauce primarily made with heavy cream and cheese, often used in pasta dishes. Béarnaise, while also an emulsion, is primarily made with clarified butter, egg yolks, and flavored with herbs like tarragon and shallots. Each of these sauces has its unique characteristics and methods of preparation, distinguishing them from Velouté.