Heat oven to 425°F and place a rack in the top third of the oven.

Scrub the potatoes under running water to remove any grit or dirt. Slice the potatoes in half lengthwise and place them in a medium saucepan.

Fill the saucepan with enough water to cover by 1 inch. Stir in 1 teaspoon salt and bring to a boil over medium-high heat. Boil for 6 minutes until easily pierced with a knife but still firm.

Drain the water and place the potatoes in a large mixing bowl. Season with salt.

Drizzle oil and sprinkle cumin over the potatoes and toss to coat well.

Spread potatoes, cut side up, on a foil-lined roasting pan or baking sheet. Roast on the upper rack, flipping halfway through, until golden brown and crispy, about 35 minutes.

Mix melted butter and grated garlic in a small bowl. Two to three minutes before the potatoes are done, pour butter-garlic mixture over them.

Turn off the oven and return the pan for 2–3 minutes to cook in residual heat, being careful not to let the garlic burn.

Remove from oven and transfer potatoes to a serving bowl.

In a small bowl, mix tamarind paste, date syrup, and lime juice.

When ready to serve, pour the mixture over potatoes and toss to coat well. Top with shallots, scallions, cilantro, and green chile if using. Serve warm.