Mix 200g of all-purpose flour and 1 tablespoon of superfine sugar. Gradually add 150ml of cold water, using just enough to make a soft dough. Chill briefly. Grate 100g of cold unsalted butter.
Roll the dough into a 12 × 16in / 30 × 40cm rectangle. Scatter half the butter over it; fold into thirds. Turn, roll again, add remaining butter and repeat the fold. Wrap and chill for 30 minutes.
Whisk 4 egg yolks, 1 tablespoon of cornstarch, and 100g of superfine sugar for the custard until pale.
Gently simmer 250ml of milk, 250ml of heavy cream, 1 split vanilla bean, 1 cinnamon stick, and 1 strip of lemon zest. Whisk into the yolks. Return to the pan; stir gently for 2-3 minutes, until slightly thickened. Strain.
Preheat the oven to 400°F / 200°C. Butter a 12-cup muffin pan. Roll the pastry into a 16 × 8in / 40 × 20cm rectangle, then roll it up tightly from a long edge. Cut into 12 equal pieces.
Flatten each piece spiral-side up and press into a muffin hole. Fill almost to the top with custard.
Bake for 30 minutes, until the pastry is golden and custard gently puffed. Cool before removing.
