When we rearranged the kitchen after installing the laminate flooring, I conjured up a countertop to replace the ancient one over a cabinet left standing in one end of the kitchen where the new refrigerator didn’t fit. This was a temporary measure until we built an additional cabinet adjacent to the old one and laid a single countertop over the whole affair. Having several short lengths of generic gray countertop left over from the Black Bathroom, laundry, and the other side of the kitchen, I butt-glued two hunks together with a small block of wood underneath as a support.
Time passes, we never did get around to building the other cabinet, and eventually the weight of the microwave and mixer bowed the poorly supported joint until it broke free and deposited the mixer on the floor.
Both pieces being bowed, I screwed some angle bracket underneath to straighten them out, clamped them together, laid a piece of tape over the joint, and match-marked the dowel locations:

Drilled holes for 1/4 dowel pins that I sliced off a length of aluminum rod (no sissy wood pins for me!):

Slobbered epoxy over the pins with enough into the holes for good adhesion, then buttered up the joint to fill the voids:

Put more tape over the countertop, sliced out the gap, and buttered up the top surface to fill the joint:

That works because JB Industro-Weld Epoxy turns out to be a nearly perfect color match:

Those angle brackets remain in place underneath the surface in the hope they’ll prevent it from bowing again. An aluminum strip (not yet installed in these pix) fills the recess below the backsplash to level it with the underside of the countertop, providing more support over the back of the cabinet case.
The whole affair took a few days, what with curing successive epoxy applications overnight. Got to use some tools that don’t often see the light of day, too, which is always good fun.
Maybe we’ll build that other cabinet some day…