all possible.

One challenge here, though, is that most counters overhang to protect your cabinet fronts from drips and spills. Your drawing shows that square - but actually you could create the overhang, too.

biggest issue I see is that you'll increase the overall height of your workspace.

You don't have to do the second one flush, you can still do an overhang, and it can be narrower

Thank you so much for your response! Smart point about the workspace height. At present there are 19 inches from cabinet top to bottom of the uppers, so 2 layers of plywood plus the slab would reduce it to 17 1/2 or a bit less which is tighter than intended. I'll check what height the range sits at for another point of comparison.

Again thank you very much for taking the time to respond and share your insight.

I don't quite understand the circumstance that keeps you from having the overhang. In any event, if the new surface isn't quite deep enough (dimension from front-to-back of new surface, can you add a backsplash and insert it down between your new surface and the back wall so as to move your new surface out and have the overhang?

Thank you John. I'm trying to avoid the countertop hanging down in front of the cabinet, since it blocks the top rail and looks odd. It's not a depth issue, there's enough slab to cover the counters. It's a height issue at the face of the cabinet. Ideally I would have bought a 3cm slab and could have laid it on top without need for a mitered/glued edge.

I'm trying to avoid the countertop hanging down in front of the cabinet, since it blocks the top rail and looks odd.

I am a bit confused. Does the countertop material actually hang down the cabinet face in your area? Here 2cm stone gets 5/8" plywood under it. The edge is then built up to the bottom of the plywood. This gives you a 1.4" countertop height which is then placed on a 34.5" cabinets for pretty close to the standard 36" cabinet height. They don't hang down the cabinet faces unless you have custom built something and asked for that.

In your pictures why are they building up your countertop face beyond the single sheet of plywood build up? Just have a smaller buildup on the face and the problem is solved.

Thank you to those who provided helpful feedback. I've resolved the matter.

" I've resolved the matter. "

@snuffy34 How? Don't leave us hanging.

I don't recommend full plywood underlayment under countertops. Cabinet grade is too expensive to use whole, so fabricators plop some roof sheathing down and call it good. Cabinet grade plywood strip underlayment over the tops of the cabinet sides, fronts, and backs is plenty and affordable. Less is more when it comes to dissimilar materials and dimensional stability.