Instructions
Begin by preheating your oven precisely to 170°C (fan) or 190°C (conventional, Gas Mark 5), ensuring it holds temperature for at least 20 minutes before baking.
Lightly dust a clean, cool surface with flour. Gently roll out the well-chilled 375g all-butter shortcrust pastry to an even thickness of approximately 2-3mm, ensuring not to overwork the dough to maintain its flakiness. Use a 7.5cm fluted cutter to meticulously cut out 18 to 20 pastry rounds. Re-roll any trimmings delicately to cut additional rounds if necessary. Carefully press these pastry rounds into two deep 12-hole tart tins, avoiding stretching the dough. Place the prepared tart shells in the refrigerator or freezer to chill for at least 15 minutes while preparing the filling; this helps prevent shrinkage during baking.
In a small pan, gently melt the 50g high-quality unsalted butter over low heat and set aside to cool slightly. In a large bowl, whisk the 2 large free-range eggs until just combined. Gradually incorporate the 175g dark muscovado sugar, 100g pre-soaked and drained premium golden raisins, 1 teaspoon pure Madagascar vanilla extract, the slightly cooled melted butter, 4 teaspoons heavy cream, and 1/4 teaspoon flaky sea salt. Mix all ingredients together thoroughly but gently to combine.
Transfer this mixture to a heavy-bottomed saucepan. Place the saucepan over medium-low heat, stirring continuously with a silicone spatula or wooden spoon for 3 to 5 minutes. Continue stirring until the mixture gently bubbles, begins to thicken noticeably, and achieves a 'nappe' consistency (it should lightly coat the back of the spoon without running off immediately). Crucially, do not boil vigorously or overcook, as this can lead to a chewy, rather than gooey, filling. Immediately remove the pan from the heat. Stir in the 50g toasted and coarsely chopped walnuts.
Spoon the warm, luscious filling into each chilled, unbaked pastry shell, ensuring the mixture is level with the top edge of the pastry. Bake in the preheated oven on the middle rack for 15 to 18 minutes.
The tarts are perfectly done when the edges of the pastry are a delicate golden brown and the filling is set around the perimeter but still exhibits a slight, enticing wobble in the very center. Remove from the oven and allow the tarts to cool in their tins for at least 10 minutes to allow the filling to set further.
Carefully transfer the tarts to a wire rack to cool completely.
For an elevated presentation, serve warm with a dusting of fine confectioners' sugar, a dollop of crème fraîche, or a sprig of fresh mint. These butter tarts are best enjoyed warm or at room temperature, offering a perfect balance of rich, sweet, and nutty flavours.