Whisk starter, water, and honey in a large bowl until dissolved, then stir in flour and salt until no dry flour remains. Cover and rest for 30 minutes.

Cook strawberries, sugar, and lemon juice over medium heat for about 8 minutes, then stir in cornstarch slurry and cook 30 seconds until thick. Cool completely.

Perform 3 sets of stretch and folds over 1.5 hours, flatten cooled dough into a rectangle, spread with filling, and fold into a letter fold shape.

Shape the loaf, place seam side down in a proofing basket, and proof at room temperature for 3 to 4 hours until puffed.

Preheat a Dutch oven at 450°F for 30 minutes, flip the loaf onto parchment, score, and bake covered 30 minutes, then uncovered 15-20 minutes.

Cool on a rack for at least 1 hour before slicing to reveal the jammy swirl.