Prepare the Dough:

1. Activate the Yeast: In a small bowl, dissolve the sugar in warm water (110°F). Sprinkle the yeast over the water and let it sit for 5 minutes, or until frothy.
2. Mix the Dough: In a large mixing bowl, combine the flour, salt, and chopped rosemary. Pour in the yeast mixture and melted butter. Stir until a dough begins to form.
3. Knead the Dough: Transfer the dough onto a lightly floured surface and knead for about 5-7 minutes, until it becomes smooth and elastic.
4. Let the Dough Rise: Place the dough in a lightly oiled bowl and cover with a clean kitchen towel. Allow the dough to rise in a warm place for about 30 minutes, or until it has doubled in size.

Shape the Pretzels:

5. Preheat the Oven: While the dough is rising, preheat your oven to 450°F (230°C) and line a baking sheet with parchment paper.
6. Divide the Dough: Once the dough has risen, punch it down to release any air bubbles. Divide the dough into 12 equal pieces.
7. Shape the Pretzels: Roll each piece of dough into a long rope, about 12 inches in length. Form the rope into a heart shape by twisting the ends together and folding them over to form a point at the bottom of the heart.

Boil the Pretzels:

8. Boil the Pretzels: In a large pot, bring 8 cups of water to a boil. Add the baking soda to the boiling water (it will bubble up). Carefully drop the shaped pretzels into the boiling water, a few at a time, and boil each for 30 seconds. Use a slotted spoon to remove the pretzels and place them on the prepared baking sheet.

Bake the Pretzels:

9. Bake the Pretzels: Brush the pretzels with melted butter and sprinkle with sea salt. Bake for 12-15 minutes, or until the pretzels are golden brown and crispy.
10. Cool and Serve: Allow the pretzels to cool slightly before serving. Garnish with extra rosemary sprigs, if desired.