In a small saucepan, whisk the water and bread flour. Cook over medium heat, whisking constantly, until it thickens into a paste. Set aside to cool.

In a stand mixer bowl, combine flour, sugar, yeast, and salt. Add milk, egg, and tangzhong. Mix on low speed for 2 minutes.

Add butter gradually while mixing. Increase speed slightly and knead for 12 minutes until smooth and elastic.

Shape dough into a ball, place in a greased bowl, cover, and rest for 20–30 minutes.

Roll dough to 3/4-inch thickness and cut with a 3-inch round cutter. Place on parchment squares.

Cover loosely and proof until doubled and puffy, about 45–65 minutes.

Heat oil to 350°F (180°C). Fry donuts 1–2 at a time for about 2 1/2 minutes total, flipping halfway.

Cool completely, roll in sugar, then fill with raspberry jelly using a piping bag. This Jelly-Filled Donuts recipe delivers perfect results every time.