Dough

1. Combine the flour, sugar, instant yeast, and salt in the bowl of a stand mixer fitted with a dough hook attachment and stir until combined
2. Add the lukewarm milk and water to the dry ingredients and mix until smooth
3. Add the butter and mix on medium speed until smooth and elastic, it will take up to 15 mins
4. Place the dough in a large oiled bowl and cover with cling wrap
5. Place in a warm place for 60 mins, or until doubled in size
6. Remove from the bowl and roll into a circle about 1.5cm/0.6 inches in thickness
7. Using a heart-shaped cutter cut out shapes of dough and place them on a baking tray lined with parchment paper
8. (Gather any remaining dough scraps into a ball and reroll it out to cut out more shapes)
9. Cover with cling wrap to proof for 30 mins, or until almost doubled in size
10. Bring a deep-fryer or heavy-bottomed pot of neutral frying oil to 280F / 140C - 300F/150C
11. Cut the parchment paper so each donut is on it's own piece of paper
12. Carefully transfer 3 donuts to the oil by holding the ends of the parchment paper
13. Fry for 2-3 mins per side, or until golden brown, removing the parchment paper after 30 seconds or so
14. Remove from the oil and drain on a wire rack or paper towel
15. Repeat with the remaining donuts
16. Add the drained donuts to the granulated sugar and roll to coat
17. Allow them to cool to room temperature.

Assembly

1. Fill a pastry bag fitted with a medium-sized piping tip with strawberry jam
2. Poke a hole in the back of the donut with a skewer and move it around to create a cavity in the donut
3. Insert the tip of the piping bag into the donut and fill it with strawberry jam
4. Repeat with the remaining donuts
5. Enjoy immediately!