Peel and cut the potatoes.

Place potatoes in pot, cover with water so water is an inch above potatoes, and season with salt.

Once a fork can go in to potatoes easily, drain potatoes and mash.

Set aside.

Heat oil in large saute pan over medium-high heat.

Saute diced onions and ginger paste for approximately 3 minutes, stirring occasionally.

Add the ground coriander, garam masala, ground cumin, salt, ground mustard, and chili powder and stir.

Add the frozen peas, stir to combine, and cook an additional 2-3 minutes.

Add the mashed potatoes and chopped cilantro, continue to cook for another 2-3 minutes.

Add water, as needed up to 1/4 cup, so that the filling mixture is moist.

Taste and adjust seasonings, as needed.

Remove from heat and allow to cool enough to handle.

Preheat oven to 400 degrees.

Unroll the thawed phyllo dough, cover with plastic wrap and a damp lightweight towel to keep it from drying out.

Peel off one sheet of phyllo dough and keep the remaining dough covered.

Lay the pastry sheet on a flat, clean surface, and brush gently with melted butter.

Fold phyllo sheet in one-third of the pastry lengthwise towards the middle.

Brush again with the butter.

Fold the last one-third to make a long triple-layered strip.

Place one rounded teaspoon of the filling mixture at one end of the strip.

Take the right corner and fold diagonally to the left, enclosing the filling and forming a triangle.

Fold again along the upper crease of the triangle, and keep folding in this manner making triangle upon triangle until you reach the end of the strip.

Brush a little butter on the dough to seal the samosa and so the outside is lightly coated in butter.

Place the samosa onto a parchment lined baking sheet and cover with another damp towel while you assemble the rest of the samosas.

Bake in the center of the oven for 20-25 minutes, or until golden and crisp, turning the samosas over halfway through the baking time.

Serve warm, garnished with extra chopped cilantro, chutney, and/or raita, as desired.