It's the nip, that little snap of lactic sharpness, that makes crème fraîche and soured cream so useful in the kitchen. The same peck of acidity that arrives with young cream cheeses – thick, spoonable labne and the delicious but difficult-to-track-down goat's curd. Their bite is present too in thick, unpasteurised, yellow double cream. None of which I would want to get through the summer without.
Earlier in the week I made a fish salad with soured cream as the dressing's main ingredient. The effect was one of richness, but with a clean edge to it that seemed just right on a sticky summer's day. The fish in question were rollmop herrings straight from a jar, whose character is a clever balance between sweet and sour. They received a creamy, slightly tart dressing similar to how they often end up in Nordic recipes, but without the almost obligatory mustard. We ate our white, silver and green salad with its finely sliced red onion, feathers of dill and crisp cucumber, as a main course with slices of toasted rye bread.
If rollmops aren't your thing, then it's a salad worth making with smoked trout or mackerel, in which case it will benefit from a few chopped gherkins too. Ssomething to raise the sharpness factor a few decibels. The sharpness of soured cream, cream cheese and crème fraîche is welcome, too, in guacamole-style dips. I made a dazzling filling for corn tortillas this week using roughly mashed Hass avocados, chopped red chillies, coriander leaves, chopped cherry tomatoes and lime juice. Afinal folding-in of soured cream lightened the filling. That said, the real stars were probably the perfect little avocados, their buttery flesh at the perfect point of ripeness, and mercifully, free of any grizzly black marks. (Can't be doing with them on bananas either.)
It was while making this that I remembered the simple pleasure of a thoughtfully ripened avocado, stoned and filled with soured cream. A 1970s bistro classic and one worth revisiting. This time I turbo charged it with a few (rinsed and dried) bottled green peppercorns and a few coriander leaves. Worth a try if you are looking for a light, fresh-tasting quickie.
It's been a week of tantalising flavours all round. There was the peaked dollop of crème fraîche adorning a slice of flourless chocolate cake, a wave of fluffy goat's curd on rye crispbread and a slice or two of smoked salmon (my current snack de jour) and a not unsuccessful experiment of a cheesecake iced with a layer of soured cream and a trickle of dark and bitter chocolate.
I guess one of the reasons I like a posset or a syllabub to finish dinner is that despite their inherent creamy quality they have a clean, fresh pinch to them, too. Rich and refreshing seems like the best of both worlds to me, the acidity immediately cutting through the cloying habit of sugar and cream. This week I swapped lemon for passion fruit in a posset-style dessert, sharpening the sugar and cream with the glowing saffron-coloured juice of ripe, dimpled passion fruits. They were expensive, probably less so if I had bought them in fours at the supermarket, so this was the ideal way of using them, in a recipe serving a minute amount to each guest. An espresso cup seems a mean receptacle for apudding, but when something is as rich as this it is just about enough. A shortbread biscuit on the side is the way to go.
Herrings, sour cream and rye toast
I use the pickled herrings that turn up in plastic containers or large jars without apology. Make your own if you fancy. They often come stuffed with onion, which should be discarded. This works as a light lunch, but is quite substantial, especially if you keep the toast hot and slice it on the thick side.
Serves 2
cucumber 250g
sea salt
red onion 1, small
dill leaves and stalks 15g
white-wine vinegar or verjuice 2 tbsp
pickled herring fillets 300g
soured cream or soft labne 200g
capers 8
rye bread 4 slices
for the top:
red onion a few slices
dill a little
Peel the cucumber and slice it thinly, each piece no thicker than a pound coin. Put the slices in a colander and scatter with salt. Set the colander over the sink and leave for an hour. The salt will draw out the juices.
Pat the cucumber slices dry with kitchen paper and transfer to a mixing bowl. Peel the onion and thinly slice half of it, finely chopping the remainder. Chop the dill fronds and stalks and toss most of them with the cucumber, the sliced and chopped onion and vinegar or verjuice.
Pat the herring dry, then slice it into short 1cm-wide strips. Add these to the cucumber. Mix the soured cream with the herring and cucumber, season with black pepper and the capers and set aside.
Make the toast then spread the herring mixture generously on top. Scatter with chopped dill and thinly sliced red onions.
Passion fruit creams
Passion fruits are generally sold when they are smooth to the touch but are not truly ripe until they are lightly pitted and wrinkled. They should still be heavy in the hand, indicating they are juicy within. Avoid the large yellow granadilla, which is often labelled passion fruit but lacks the sharpness of the little ones.
Makes 6-8 espresso cups
passion fruits 16
double cream 500ml
caster sugar 150g
lemon juice 35ml
Cut the passion fruit in half and scrape out the seeds and juice into a small sieve balanced over a measuring jug or bowl. Let the juice drip through, then rub the seeds against the sieve with a teaspoon to get as much of the pulp through as you can. Set the juice aside in a cool place and reserve a few of the seeds for later.
Put the cream and caster sugar in a saucepan and bring to the boil, stirring occasionally to dissolve the sugar. Lower the heat and leave to bubble for three minutes, stirring occasionally, taking care the mixture doesn't boil over. Put the 35ml of lemon juice in a measuring cup then make the quantity up to 75ml with the reserved passion fruit juice. Keep the remaining juice cold.
Remove the cream mixture from the heat, stir in the lemon and passion fruit juice and leave to settle for a few minutes. Pour into 6 to 8 espresso cups or very small glasses. I like to stir a few of the reserved passion fruit seeds into the mixture for a contrast in texture (say half a dozen per cup) but that is up to you. Cool then refrigerate for at least a couple of hours before serving.
Just before you serve the creams, spoon a little puddle of the reserved passion fruit juice and a few seeds over the top. As each diner digs in with their teaspoon, the juice will trickle down into the depths of the cream.
Email Nigel at nigel.slater@observer.co.uk or visit theguardian.com/profile/nigelslater for all his recipes in one place
