Fill a tea kettle with water and bring to a boil. Remove from the heat and set aside.

Put 1 cup sugar and 2 tablespoons of water into a saucepan over medium heat and bring to a boil, swirling the pan to combine the sugar and water. Do not stir. Let boil until dark amber in colour, swirling the pan occasionally to caramelize evenly, about 10 minutes total. Immediately pour caramel into a 9- by -5-inch loaf pan and swirl to coat the bottom evenly. Set aside to harden.

Heat oven to 325°F.

Combine milk, lemon zest, salt and the remaining 1 1/4 cups sugar (I already reduced the sugar; you may wish to reduce it further) in a saucepan over low heat. Cook, stirring, until the milk is hot and sugar has melted, but do not bring to a boil. Remove the lemon zest and set it aside to cool.

Combine eggs, egg yolks, and vanilla in a blender and blend on low speed until smooth. With the blender running (on low), very slowly pour the warm milk (if it is too hot, the eggs will cook/curdle) mixture into the eggs (I transferred my milk to a pitcher with a spout to allow for slow pouring). Pour the egg-milk mixture into the caramel-lined pan.

Place the loaf pan in a 9-inch by 13-inch baking dish. Pour enough hot water from the tea kettle into the baking dish until it comes about halfway up the sides of the loaf pan. Place in the oven and bake 65 minutes, until the flan is set but still quite jiggly in the centre. Remove flan from the water bath and cool on a rack for 30 minutes. Refrigerate, uncovered, until cold and firm, at least 8 hours or up to 3 days.

To unmold, run a thin sharp knife around the edges. Centre a rimmed platter upside down on top of the pan and, holding both, quickly flip the pan and plate together. Remove the pan, watch the caramel flow, and serve chilled in slices.