Steps
1. In a small bowl, beat the unsalted butter until creamy.
2. Gradually add the granulated sugar and continue to beat until light and fluffy.
3. Mix in the brewed coffee, milk, vanilla extract, and a pinch of salt until smooth.
4. Taste and adjust sweetness if necessary by adding more sugar.
5. Serve the buttercream in a small dish and enjoy it as a dip with cookies or spread it on a slice of cake.