In a small saucepan over low heat, whisk together egg yolks, lemon juice, and water until slightly thickened (2–3 minutes).

Gradually whisk in melted butter, a little at a time, until thick and smooth.

Stir in chopped sorrel and season with salt. Keep warm over low heat, stirring occasionally.

Slice focaccia into thick pieces. Heat a skillet over medium heat and melt a knob of butter.

Toast the focaccia on both sides until golden brown. Remove and let cool slightly.

For the first version, spread crème fraîche on the focaccia, top with trout roe, dill, and sliced shallot.

For the second, spoon warm sorrel béarnaise onto focaccia, then top with Osetra caviar. Garnish with sorrel flowers and Maldon salt.