Heat the milk in a saucepan until hot, but not boiling
In a medium saucepan, whisk together the egg yolks, sugar, and flour until pale and smooth
Slowly add the vanilla and warm milk, a little at a time, whisking constantly to avoid lumps
Place over medium heat and stir continuously until the cream thickens and begins to bubble gently. Reduce heat and cook for 1–2 more minutes until smooth and glossy
Transfer to a glass bowl, cover with plastic wrap (pressed against the surface to prevent a skin from forming), and let cool completely
Preheat the oven to 350°F (180°C). Grease a mini cheesecake pan or a jumbo muffin pan
In a large bowl, whisk together the eggs and sugar until light and airy. Slowly add the butter and milk, whisking continuously
Stir in the lemon zest, then sift in the flour, baking powder, and salt. Mix until just combined; do not overmix
Pour the batter into the prepared pan. Drop spoonfuls of cooled custard cream evenly across the surface
Bake for about 40 minutes, or until golden on top and a toothpick inserted in the center comes out clean
Allow to cool, remove from the pan, and dust generously with powdered sugar before serving
