Preheat oven to 350°F (180°C). Thoroughly drain the Irish stew using a fine-mesh strainer to remove excess liquid.
Whisk together the egg and 2 teaspoons of water in a small bowl to create an egg wash.
In another small bowl, mix the garlic powder, sea salt flakes, and black pepper.
Lightly spray pie tins with canola oil to prevent sticking.
Let puff pastry sit at room temperature for 2-3 minutes, then cut into pieces sized for your pie tins for bases and tops.
Press pastry bases gently into the oiled tins, fitting them to the bottom and sides without stretching.
Divide the drained stew evenly among the pie tins, filling each about halfway.
Brush the rim of each pastry base with some egg wash to help seal the edges.
Place pastry tops over the filled pies and press edges firmly to seal.
Brush the tops generously with remaining egg wash for a glossy finish.
Sprinkle black sesame seeds evenly on the pastry tops, pressing gently to adhere.
Cut 2-3 small slits in the center of each top to allow steam to escape.
Bake pies at 350°F (180°C) for 40 minutes until pastry is golden and puffed.