Combine whole eggs and yolks, sugar, and lemon juice in a heatproof bowl and set over a pan of simmering water. Cook, whisking constantly, until mixture is thick enough to coat the back of a spoon. Remove from heat. Add butter, a few pieces at a time, whisking until smooth after each addition. Strain through a fine sieve into another bowl, and cover with parchment paper or plastic wrap, pressing it directly on surface to prevent a skin from forming. Refrigerate until chilled and firm, at least 2 hours (or up to 2 days).