Step 1

Whisk all-purpose flour, rye flour, caraway seeds, and yeast together in bowl of stand mixer. Whisk 1 2/3 cups water, oil, and molasses in 4-cup liquid measuring cup until molasses has dissolved.

Step 2

Fit stand mixer with dough hook; add water mixture to flour mixture and knead on low speed until cohesive dough starts to form and no dry flour remains, about 2 minutes, scraping down bowl as needed. Cover bowl tightly with plastic wrap and let dough rest for 20 minutes.

Step 3

Add salt to dough and knead on medium-low speed until dough is smooth and elastic and clears sides of bowl, about 5 minutes.

Step 4

Transfer dough to lightly floured counter and knead by hand to form smooth, round ball, about 30 seconds. Place dough seam side down in lightly oiled large bowl, cover tightly with plastic, and let rise until doubled in size, 1 1/2 to 2 hours.

Step 5

Transfer dough to lightly floured counter and gently press into 8-inch disk, then fold edges toward middle to form round. Cover loosely with plastic and let rest for 15 minutes.

Step 6

Adjust oven racks to middle and lowest positions, place baking stone on upper rack, and heat oven to 450 degrees. Line overturned rimmed baking sheet with parchment paper and dust lightly with rye flour. Gently press and stretch dough into 12 by 9-inch oval, with short end of oval facing edge of counter. Fold top left and right edges of dough diagonally into center of oval and press gently to seal. Fold point of dough into center of oval and press seam gently to seal. Rotate dough 180 degrees and repeat folding and sealing top half of dough.

Step 7

Fold dough in half toward you to form rough 8 by 4-inch crescent-shaped loaf. Using heel of your hand, press seam closed against counter. Roll loaf seam side down. Tuck ends under loaf to form rounded torpedo shape. Gently slide your hands underneath loaf and transfer, seam side down, to prepared sheet.

Step 8

Spray sheet of plastic with vegetable oil spray and cover loaf loosely. Let loaf rise until increased in size by about half and dough springs back minimally when poked gently with your knuckle, 45 minutes to 1 1/4 hours.

Step 9

Place empty loaf pan on bottom oven rack. Using sharp paring knife or single-edge razor blade, make six to eight 4-inch-long, 1/2-inch-deep slashes with swift, fluid motion across width of loaf, spacing slashes about 1 inch apart. Pour 2 cups boiling water into empty loaf pan in oven.

Step 10

Slide parchment and loaf from sheet onto baking stone. Bake until deep golden brown and loaf registers 205 to 210 degrees, 25 to 30 minutes, rotating loaf halfway through baking. Transfer loaf to wire rack.

Step 11

Whisk cornstarch and remaining 1/2 cup water in bowl until cornstarch has dissolved. Microwave, whisking frequently, until mixture is thickened, 1 to 2 minutes.

Step 12

Brush top and sides of loaf with 3 tablespoons cornstarch mixture (you will have extra cornstarch mixture). Let cool completely, about 3 hours, before slicing and serving.