Mix the dough. Combine flour, salt, and yeast the bowl of a stand mixer fitted with a dough hook. In a separate bowl, whisk together warm milk, honey, vanilla, and egg. Pour the wet ingredients into the dry ingredients. Mix on low speed until the dough comes together in a shaggy messy ball on the dough hook, about 3-5 minutes. The dough will look dry at first, but will hydrate as it mixes. Be patient!

Knead the dough. Increase speed to medium-low and knead the dough for 5-7 minutes, ideally until it passes the windowpane test. If it doesn't pass, cover and let the dough rest for 5 minutes, knead 1 minute more, then proceed to the next step.

Add the butter 1 tablespoon at a time. With the mixer running on medium-low, add the butter one tablespoon at a time. Let each piece fully incorporate before adding more. Pause the mixer to scrape the butter down into the bowl occasionally as needed. It can take up to a minute per piece of butter. Be patient!

Knead the dough again. Increase speed to medium and knead until the dough is smooth, shiny, and passes the windowpane test again, about 5-7 minutes.

Cover and rise. Tuck the edges of the dough under so you have a nice ball with a smooth top. Place in a lightly greased container and let rise in a warm spot for 1 hour until doubled in size, then 1-24 hours in the fridge to cool it down before cutting. Alternately, place it in the fridge immediately and let it rise for 3-24 hours in the fridge before cutting.

Roll out the dough. Turn the chilled brioche dough out onto a clean, lightly floured work surface. Use your hands to gently flatten the dough trying to avoid any big wrinkles or creases in the surface. Roll the dough out to about ¼ inch thick, dusting lightly with flour as needed to prevent sticking.

Cut the donuts. Use a 2¼"-2½" round cutter to cut as many donuts out of the dough as possible. Get them as close to each other as possible to get the most out of the dough. Use a 1" cutter to cut donut holes out of the scrap dough.

Final Rise. Arrange the donuts, donut holes, and any scrap dough on a parchment lined sheet pan, cover loosely with plastic wrap, and let rise at room temperature for 45-60 mins, until the donuts are looking a little bit puffy.

Heat the oil. Toward the end of the rise time, begin heating about 3-4 inches of oil in a large pot or Dutch oven, using a candy thermometer or frying thermometer to bring the oil to 350°F. Line a second sheet pan with paper towels and place a wire cooling rack inside it.

Fry the donut holes. Use a wire spider to gently lower 4-5 donuts at a time into the oil all at once. Fry each batch for 4-5 minutes total, flipping the donuts every 30-60 seconds or once at the halfway mark. Adjust the heat as needed to maintain an oil temperature of 350°F. Remove the donuts to the cooling rack to drain and cool.

Make sure you have paper towels nearby to wipe off the piping bag and to wipe the donuts if any jelly overflows while you're filling them.

Poke the holes. Use a paring knife to carefully poke a hole through the side of each donut. Wiggle the knife around, back and forth inside the donut to create a pocket for the jelly.

Fill with jelly. Fill a small piping bag with jelly. Snip off a small bit at the end and insert the tip of the piping bag into the donut hole. Gently squeeze from the top of the piping bag (where it's twisted to keep the jelly in) to fill the donut with jelly. Slowly pull the piping bag out of the donut as you fill it.

Dust with powdered sugar. Arrange the jelly donuts on the wire cooling rack so their bottom sides are facing up. Dust with powdered sugar. Flip them over and dust the top sides with powdered sugar too. Serve immediately!