In a bowl, combine the yeast, sugar, and 1/4 cup of warm water.

Let the mixture stand for 10 minutes to activate the yeast.

In a separate bowl, whisk together the rye flour, 1/2 cup of all-purpose flour, caraway seeds, coffee, onion powder, salt, and fennel seeds.

In a saucepan, combine 1 cup of water, vinegar, molasses, chocolate, and margarine.

Heat the mixture over low heat until the margarine and chocolate are melted.

Stir the molasses mixture into the rye flour mixture.

Add the yeast mixture and stir with a wooden spoon for 2 minutes.

Gradually add the remaining all-purpose flour (1/2 cup at a time) until a soft dough forms.

Transfer the dough to a floured work surface.

Let the dough rest for 15 minutes.

Knead the dough for 15 minutes.

Place the dough in a bowl coated with vegetable oil.

Let the dough rise for 1 hour, or until doubled in size.

Preheat the oven to 350°F (175°C). Coat a baking sheet with oil.

Shape the dough into a ball and place it on the prepared baking sheet.

Bake for 50 minutes, or until the bread sounds hollow when tapped.

In a saucepan, bring the cornstarch and 1/4 cup of water to a boil.

Cook for 1 minute, stirring constantly.

Brush the cornstarch mixture over the top of the loaf.

Bake for an additional 2 to 3 minutes.

Cool the bread on a wire rack.