Step 1

Place 4 tablespoons unsalted butter in a 2-cup glass measuring cup or medium microwave-safe bowl. Microwave on high until mostly melted, 30 to 45 seconds. Stir until the butter is completely melted.

Step 2

Place 2 large egg yolks in a small bowl and whisk with a fork to break up. Squeeze the juice from 1/2 medium lemon. Add the yolks, 1 tablespoon of the lemon juice, and 1/4 cup heavy cream or half-and-half to the melted butter and stir until combined.

Step 3

Microwave in 15-second bursts, whisking between each burst, until slightly thickened but still pourable (about 185ºF), 1 to 1 1/2 minutes total.

Step 4

Add 1/2 teaspoon Dijon mustard and whisk to combine. For béarnaise, whisk in 1 tablespoon A1 steak sauce. Taste and season with more lemon juice and kosher salt as needed. Serve warm.