Pi Day Experiment
Proceed at your own risk. This is not a well-tested recipe. This is a I-made-it-once-and-it-worked-for-me recipe. I may very well be contributing to science’s replication crisis by posting it. Baking IS chemistry, after all. But it’s Pi Day, folks, and I feel a little experimentation fits with the spirit.
So, how did this recipe come about. Well, last year I was searching for traditional Irish desserts to serve on St. Patrick’s Day. It really is a bummer to see the internet awash in green food coloring and random foolery soaked in Bailey’s around that holiday. In my search, I came across a dessert that seemed nothing short of magic – lemon posset. Possets have their roots in medieval Ireland and England. However, the original recipe was something like milk curdled with booze. Jesus. Really? OK. Moving on.
It was alleged to have medicinal properties (no.) and was served to the likes of King Charles I. It was even given shout outs by Shakespeare in both Hamlet and The Merry Wives of Windsor. For example, in the latter, The Bard wrote “Yet be cheerful knight: thou shalt eat a posset to-night at my house; Where I will desire thee to laugh at my wife.” I don’t know what’s going on there, but inviting someone to your house to drink curdled milk while they laugh at your wife sounds like a jerk move.
Anyway, over the centuries, the recipe evolved, mercifully, to cream thickened with ground nuts, egg yolks, biscuits and bread. You know, essentially what we would recognize as being akin to modern custards and puddings.
At some point, however, someone discovered the genius alchemy that is the lemon posset. Made from simply boiling cream, sugar and lemon zest and then mixing with fresh lemon juice, the result is silky, and lush and yet refreshing with a texture akin to crème brulee. How does it work? Boiling the cream evaporates any water present and leaves behind the fat. Then, acid of the lemon juice thickens the cream. Because of the high fat content, the result is pudding-like rather than curdled.
So, no tempering eggs which I hate. No baking in a water bath. No thickeners like flour, cornstarch or gelatin. No fillers, no fuss. Yes, please. Oh! And, as I later discovered, it freezes beautifully. Bonus. (Why freeze it? Well, the posset does thicken, but not enough to be sliceable which is kind of a requisite for a tart. Freezing allows for that and yields a texture that is glorious; much like a semi-freddo.)
Once I settled on the filling, I had to consider the crust. Because of the creaminess and richness of the posset, I wanted something nutty, crisp and light for the base. Just as I wanted to avoid the tediousness of tempering eggs, so too did want to avoid futzing with a traditional pastry dough. Something that could be pressed-in and that wasn’t too sweet (like many cookie crusts are). Brown butter shortbread ticked all the boxes.
I could have stopped right there. It would have been perfectly lovely, but sometimes I can’t resist gilding the lily. Enter the blackberry sauce. I am just a sucker for blackberries. They look like gorgeous little jewels and their sweet-tart flavor is addictive. As for the role this sauce plays in the tart, it brings a welcome freshness and acidity to the party. The posset certainly has acidity of it’s own, but the freshness of the lemon is tempered by the richness of the cream. This blackberry sauce is the remedy.
So here it is. A work in progress. I make no guarantees to the results but, written as is, it works for me. If you try it and things are hinky, do let me know. I will continue experimenting with this recipe and update it with any changes or improvements. I posit, however, I will be making this all summer long.
Happy Pi Day, everyone!
Frozen Lemon Cream Tart with Brown Butter Shortbread and Blackberry Sauce
Lemon Posset Filling
- 4 cups heavy cream
- 260 g granulated sugar 1 1/3 cups or 8 1/3 ounces
- 2 tablespoon grated lemon zest
- ¾ cup lemon juice
Brown Butter Shortbread Crust
- 113 g unsalted butter
- 65 g granulated sugar
- 1 teaspoon lemon zest
- 130 g all-purpose flour
- Pinch of salt
- 12 oz fresh blackberries divided
- 50 g sugar
- 3 tablespoons water
- 2 tablespoons fresh lemon juice
- 1 tablespoon lemon zest
To Make the Filling
Combine cream, sugar, and lemon zest in medium saucepan and bring to boil over medium heat. Continue to boil, stirring frequently to dissolve sugar. If mixture begins to boil over (and it WILL even if you watch it like a hawk), briefly remove from heat. Cook until mixture is reduced to 4 cups, about 12-16 minutes.
Off heat, stir in lemon juice. Let sit until mixture is cooled slightly and skin forms on top, about 20 minutes. Strain through fine-mesh strainer into bowl; discard zest.
Transfer to a shallow baking dish (I used a 9×13 one) and refrigerate uncovered, until set, at least 3 hours. While the filling chills, make, bake and cool the tart crust.
Once chilled, pour into the baked and cooled tart crust. Transfer tart to freezer and freeze until firm about 4 hours or overnight.
To Make the Crust
Melt butter over medium heat. Continue to cook, stirring constantly, until deep golden brown, about 11 minutes. Immediately pour browned butter into a large bowl, and let cool to room temperature, about 10 minutes.
Position rack in center of oven with a parchment lined baking sheet and preheat to 375°F.
Make the browned butter: Melt butter over medium heat. Continue to cook, stirring constantly, until deep golden brown, about 11 minutes. Immediately pour browned butter into a large bowl, and let cool to room temperature, about 10 minutes.
Using rubber spatula or fork, mix browned butter, sugar, salt and lemon zest in medium bowl. Add flour and stir until incorporated. Transfer dough to 9-inch-diameter tart pan with removable bottom. Using fingertips, press dough evenly onto sides and bottom of pan. Using the tines of a fork, prick the bottom of the crust all over. This process is known as docking and will keep the bottom from puffing up too much during baking
Bake crust until golden, about 18-20 minutes. Transfer crust to rack and cool in pan.
To Make the Sauce
Bring 6 oz. blackberries, sugar, water, lemon juice, and lemon zest to a boil in a small saucepan over medium-high heat. Reduce heat to low, and simmer, stirring occasionally, 8 to 10 minutes or until mixture has thickened and berries begin to break down. Remove from heat, and stir in remaining 1 cup blackberries. Cool completely (about 1 hour); cover and chill until ready to use.