Preheat oven to 400°F at step 8. Line 2 large baking sheets with parchment paper.
Combine cumin, coriander, salt, and pepper in a bowl. Set aside.
Trim fat off chicken and cut into small cubes. Finely chop onion, mince garlic, and finely cube the potatoes. Grate 2 Tbsp cold butter. Finely chop fresh herbs if you like herbs.
In a bowl, combine the chicken, onions, garlic, herbs, and potatoes. Add the seasoning mixture and mayo, and shredded butter and mix.
Unwrap and unroll the phyllo dough and take 3 to 4 sheets. Place one sheet onto the working surface. Lightly brush with the melted butter, continue with all 4 sheets. Using a pizza cutter, cut the sheets in half lengthwise, creating two equal parts. Add a generous portion of the filling to the corner end of each rectangle, leaving room around the filling. Fold over creating a triangle and press down to seal the edges so the filling doesn’t escape. Keep folding until you reach the end of the sheet, placing the edge of dough on the bottom of the triangle.
Continue with remaining ingredients. Brush tops of triangles with butter and sprinkle with sesame seeds.
Place onto baking sheet and cover with foil.
Bake for 18 minutes coved, remove foil and bake an additional 10-12 minutes uncovered.