What is a mixture of egg yolks and heavy cream that enhances sauce flavor and texture?

The mixture of egg yolks and heavy cream that enhances sauce flavor and texture is known as a liaison. This combination serves as a thickening agent and adds richness to sauces, particularly in classical French cuisine. When incorporated into a sauce, the liaison not only thickens but also gives a velvety texture, making the sauce more luxurious and palatable.

In culinary practice, a liaison is often used in cream sauces or soups to create a more refined and harmonious flavor profile. It is crucial to temper the liaison gradually with the hot sauce to prevent the egg yolks from scrambling, ensuring a smooth and creamy consistency.

The other options do not fit this description. Beurre blanc is a butter-based sauce made with wine and vinegar and does not contain egg yolks. Roux is a mixture of flour and fat used as a thickening agent, and Béarnaise is a sauce made from emulsified egg yolks, butter, and vinegar flavored with herbs—although it does contain egg yolks, it does not include heavy cream as a primary ingredient. Hence, the liaison stands out as the correct answer for the mixture comprising egg yolks and heavy cream used to enhance sauces.