Preparation

Make the pastry

In a food processor, pulse the flour, sugar, and salt. Lift off the lid, scatter the butter and lard on top of the dry ingredients, then close and pulse again until the fat is cut into large pea-size pieces, about 8 pulses. Add enough ice water to the vinegar to make
1/2 cup (120 ml) total. With the motor running, and in a thin, steady stream, pour the liquids through the feed tube. Stop the machine as soon as the dough comes together; the sound of the processor will change as it does. You might not need all the water or you might need a little bit more. You want to hydrate the dough but not make it damp. The mixture should be crumbly and light, and just hold together when squeezed. Turn the dough out onto a large cross of plastic wrap, then use the wrap to shape it into a disk. Wrap tightly, then refrigerate for at least 2 hours or up to 1 day before using. The dough can also be frozen for up to 2 months.

Place a rack in the lower third of the oven and preheat to 400°F. Working with half the dough at a time, roll to a scant 1/4-inch thickness on a lightly floured work surface. Using a 3-1/2- to 4-inch cookie cutter, cut 6 circles of dough. Chill on a parchment-lined baking sheet while rolling and cutting the second half of dough. Add these to the baking sheet and chill for
5 minutes more.

Lightly grease a standard 12-cup muffin tin. Take out one of the chilled rounds, starting with the ones that chilled the longest. Gently fit into one of the cups of the muffin tin, pleating as needed. Repeat with the remaining rounds. Place the muffin tin in the refrigerator while you make the filling. Place a bare baking sheet in the oven to preheat.

Make the filling

Melt the butter in a medium saucepan over low heat. Remove from the heat. Using a silicone spatula or wooden spoon, cream together the butter and sugar. (Do not use a whisk or electric mixer as these will incorporate air, which makes for a foamy finish.) Stir in the egg until incorporated. Add the corn syrup, vanilla bean paste, malt vinegar, and salt. Stir until just combined.

Divide the walnuts and raisins evenly among the empty tart shells. Pour the filling over. (The shells will be about two-thirds full.)

Place the tray on the hot baking sheet in the oven. Bake for 10 minutes, then reduce the oven temperature to 375°F. Continue baking until the pastry is golden and the filling is bubbling at the edges, 12 to 15 minutes more. Let cool in the pan for 10 minutes, then run a small offset spatula or thin knife around the edge to prevent sticking. Serve warm, or let cool to room temperature in the tin.

To give the tarts a subtle sheen, dip a dry brush into pearl or luster dust, then gently highlight the high points of the filling and crust.

Store up to 4 days in an airtight container the fridge. Serve cold or at room temperature (preferred).