Doughnuts with Grapefruit Curd and Citrus Sugar

Cook, whisking almost constantly, until curd is thickened, 6–8 minutes.

Remove from heat and whisk in butter, adding a few pieces at a time.

Transfer to a nonreactive bowl and press a piece of plastic wrap directly onto surface of curd.

Chill until set up and very cold, at least 4 hours and up to 12 hours.

Combine sugar and zest in a small bowl.

Let sit uncovered 12 hours to dry out. (You can also microwave on high in 15-second intervals, stirring and letting cool slightly between intervals, until dehydrated.).

Transfer to a blender and blend until powdery. (Or, work zest into sugar with your fingers; just make sure to break up any clumps.).

Heat milk in a small saucepan or microwave until just warm (you want it to be between 105°F and 110°F).

Transfer to the bowl of a stand mixer and scrape in vanilla seeds; reserve pod for another use.

Add 1 Tbsp. sugar and sprinkle yeast over.

Let sit until yeast starts to foam, about 5 minutes.

Add egg, egg yolk, honey, lemon zest, salt, and remaining 2 Tbsp. sugar.

Mix gently with a wooden spoon until barely combined.

Add 2 3/4 cups flour and knead with a dough hook on medium-high speed until dough comes together into a mass that no longer sticks to the sides of bowl and is beginning to climb up the hook, about 5 minutes. (Dough should spring back immediately when pressed.) Reduce speed to medium-low; add butter a couple of pieces at a time, working in completely after each addition.

Turn out dough onto a work surface and knead with your hands until smooth and springy, about 2 minutes.

Transfer to a very lightly oiled bowl, cover with plastic wrap, and let rise in a warm spot until doubled in volume, about 2 hours.

Turn out dough onto a lightly floured surface and roll out 1/2" thick.

Cut out doughnuts with cutter, twisting cutter to release them.

Reroll any scraps.

Transfer to a very lightly floured parchment paper–lined baking sheet.

Cover with a kitchen towel; let sit in a warm spot until slightly puffed and dough springs back lightly when pressed, 40–45 minutes.

Fit a wide heavy pot with thermometer; pour in oil to come at least 2" up sides.

Heat over medium-high until thermometer registers 325°F.

Fry 3 or 4 doughnuts at a time, turning halfway through, until deep golden brown, about 6 minutes per batch.

Transfer to a wire rack set inside a rimmed baking sheet; let cool.

Using a paring knife, poke a hole in the top of each doughnut, being careful not to push through to the opposite side.

Transfer grapefruit curd to a piping bag or resealable plastic bag (snip off one corner) fitted with a 1/4” round tip.

Fill doughnuts with grapefruit curd, then coat generously with citrus sugar.

Citrus sugar can be made 3 days ahead.

Store airtight at room temperature.