Filling:
Place the mushrooms in a food processor fitted with a steel blade. Pulse until the mushrooms resemble couscous, about 10 pulses. If you don’t have a food processor, mince by hand with a knife. Transfer the minced mushroom to a large bowl and mix with the ground beef.

Peel and quarter the onion before placing it in the food processor. Pulse until minced. Alternatively, the onion can be minced by hand.

In a large skillet, heat the oil over medium-high heat. Cook the onions until soft, about 5 minutes. Add the ginger and garlic and cook 1 minute. Add the cumin, coriander, garam masala, turmeric, salt and dried chilli flakes. Cook 1 minute, stirring constantly to ensure the spices are well distributed.

Add the mushroom/beef combination and cook 5 to 7 minutes or until the beef is no longer pink.

Place the beef mixture in a sieve and allow to drain five minutes to remove excess liquid. Too much moisture in the filling can cause the samosas to burst while cooking. Transfer the strained mixture to a large bowl, stir in the lemon juice, peas, corn and cilantro. Allow to cool. The filling can be covered and refrigerated for up to 3 days.

Wrapping:

When you’re ready to wrap the filling, preheat the oven to 350°F.

Unwrap the phyllo and it lay flat. Cover it with a slightly damp tea towel to prevent it from drying out. Remove one sheet, and brush lightly with oil using a pastry brush. Fold in thirds lengthwise so you have a long, narrow strip three layers thick. Place 1/4 cup filling at the bottom of the phyllo strip, about 1/2 inch from the left edge. Fold the bottom right corner over the filling to form a triangle. Fold the filling up the sheet of phyllo, maintaining the triangle form. Place on a baking sheet, brush with more oil and sprinkle with black sesame seeds, if using. Repeat with remaining phyllo and filling.

Bake for 20 to 25 minutes or until the pastry is golden brown. Serve hot as is or with tamarind sauce.