Warm the whole milk and water in a saucepan over low heat until just steaming, then add unsalted butter and honey until melted. Sprinkle in the active dry yeast and let sit for about 5–10 minutes until frothy.

In a large bowl, combine the yeast mixture with lightly beaten eggs, granulated sugar, salt, freshly grated nutmeg, and half of the all-purpose flour. Mix until smooth and well-combined.

Transfer the dough to a greased bowl, cover with a towel, and place in a warm spot for about 1 hour, or until it doubles in size.

Turn the dough onto a floured surface and roll it out to about ½ inch thick. Cut out doughnut shapes and let them rest for another 30 minutes.

Heat vegetable oil in a deep pot to 365-370°F. Carefully place the doughnuts in the hot oil, frying each for 1-2 minutes on each side until golden brown.

In a saucepan over medium-low heat, whisk together freshly squeezed lemon juice, granulated sugar, and cornstarch. Gradually add egg yolks while continuously stirring, cooking until thickened.

In a bowl, combine chilled lemon curd and mascarpone cheese until smooth. Transfer to a piping bag and fill each cooled doughnut.

Whisk together mascarpone cheese, powdered sugar, and enough milk to achieve a pourable consistency for the glaze. Drizzle over filled doughnuts and sprinkle with granulated sugar.