The secret to creating a terrific crust on a well-marbled cut of beef: rubbing on a salty-sweet spice mix and letting the meat air dry before grilling.
In a small skillet, toast the allspice, peppercorns, cumin seeds, cinnamon and cloves over moderately high heat until fragrant. Transfer to a spice grinder and let cool completely. Grind to a powder and transfer to a small bowl. Stir in the paprika, chipotle and ancho powders, salt and sugar. Sprinkle 2 tablespoons of the adobo rub all over the rib eye and let stand at room temperature for 30 minutes.
Preheat the oven to 350°. Wrap the garlic in foil and bake for about 30 minutes, until soft.
Over an open flame or under a preheated broiler, roast the poblano until charred all over; let cool. Peel, seed and stem the poblano and coarsely chop it. Transfer to a blender. Squeeze the soft garlic cloves from their skins into the blender. Add the lime juice, egg yolk, serrano, cumin and cilantro and puree. With the machine on, slowly pour in the 1/2 cup of oil until emulsified. Season with salt.
Light a grill. Oil the grate. Grill the steak over moderately high heat for 6 minutes per side, until charred outside and medium-rare within. Let the steak rest for 5 minutes. Slice and serve with the aioli.
Any leftover adobo rub can be stored at room temperature for up to a month.