Adapted from Kitchen Riffs.
2 egg yolks
1 stick butter (about 150 grams)
1 table spoon lemon juice
1 tea spoon water
Salt & Pepper
From the butter, cut four small pieces and reserve for later.
Cut the rest of the butter into pieces of about a tablespoon each and melt it.
Place egg yolks into a small saucepan. Using a whisk or a fork, whip egg yolks in the pan for a minute or until they are thick and pale yellow. Add the lemon juice and water and whisk for about more 30 seconds.
Put the saucepan with the egg yolk mixture over low heat ( I always use the lowest heat and cook them over simmering water, because I want to make sure they do not curdle – just make sure that the saucepan does not touch the simmering water. Add 2 of the reserved pieces of butter, and whisk at a moderate pace. The butter will melt as you whisk, helping to avoid curdling the eggs. Beat until egg yolks have thickened. Remove egg yolk mixture from heat and add the rest of the butter – piece by piece, while beating. Then add the melted butter, which should be at least warm and beat again until the sauce thickens completely.
Taste and season with salt and pepper.