In a Black Russian cocktail, which ingredient is used alongside vodka?

In a Black Russian cocktail, Kahlua is the essential ingredient used alongside vodka. Kahlua is a coffee liqueur that provides the drink with its distinct flavor profile, combining the robustness of coffee with a hint of sweetness. This combination of vodka and Kahlua creates a simple yet elegant cocktail that highlights the rich notes of the coffee while allowing the purity of the vodka to shine through.

The other ingredients listed do not align with the traditional composition of a Black Russian. Cream, peach nectar, and triple sec are not components of this cocktail and would significantly alter its intended flavor and character. Thus, the selection of Kahlua as the key ingredient reinforces the authenticity and classic taste of a Black Russian.