A gas turbine combustor assembly, comprising: a primary combustion chamber in fluid communication with a primary fuel injector and a primary air inlet; and a torch ignitor coupled to the primary combustion chamber, the torch igniter comprising: an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source, the igniter body comprising: an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall, the side wall defining an interior cavity between the first and second end walls; and a premixing cup residing within the interior cavity comprising a cylindrical wall radially surrounding the auxiliary fuel injector and an auxiliary air inlet, the cylindrical wall of the premixing cup protruding axially outward relative to the first end wall of the auxiliary combustion chamber through a portion of the interior cavity to delineate a premixing zone radially inward of the cylindrical wall and a recirculation zone radially outward of the cylindrical wall, with the ignition source residing on the side wall of the auxiliary combustion chamber at a position proximate the recirculation zone. a primary combustion chamber in fluid communication with a primary fuel injector and a primary air inlet; and a torch ignitor coupled to the primary combustion chamber, the torch igniter comprising: an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source, the igniter body comprising: an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall, the side wall defining an interior cavity between the first and second end walls; and a premixing cup residing within the interior cavity comprising a cylindrical wall radially surrounding the auxiliary fuel injector and an auxiliary air inlet, the cylindrical wall of the premixing cup protruding axially outward relative to the first end wall of the auxiliary combustion chamber through a portion of the interior cavity to delineate a premixing zone radially inward of the cylindrical wall and a recirculation zone radially outward of the cylindrical wall, with the ignition source residing on the side wall of the auxiliary combustion chamber at a position proximate the recirculation zone. an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source, the igniter body comprising: an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall, the side wall defining an interior cavity between the first and second end walls; and a premixing cup residing within the interior cavity comprising a cylindrical wall radially surrounding the auxiliary fuel injector and an auxiliary air inlet, the cylindrical wall of the premixing cup protruding axially outward relative to the first end wall of the auxiliary combustion chamber through a portion of the interior cavity to delineate a premixing zone radially inward of the cylindrical wall and a recirculation zone radially outward of the cylindrical wall, with the ignition source residing on the side wall of the auxiliary combustion chamber at a position proximate the recirculation zone. an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall, the side wall defining an interior cavity between the first and second end walls; and a premixing cup residing within the interior cavity comprising a cylindrical wall radially surrounding the auxiliary fuel injector and an auxiliary air inlet, the cylindrical wall of the premixing cup protruding axially outward relative to the first end wall of the auxiliary combustion chamber through a portion of the interior cavity to delineate a premixing zone radially inward of the cylindrical wall and a recirculation zone radially outward of the cylindrical wall, with the ignition source residing on the side wall of the auxiliary combustion chamber at a position proximate the recirculation zone.