Yeah, just take the top off and put one on that extends 3” further front to back.

I would hang shelves on the wall behind the cart. Pull the cart out to meet the countertop edge. Look for a shelf unit or even floating shelves. The lower shelf should slightly overlap the back of the cart. The higher shelves may be useful for storing other items.

Good idea, though I'm not sure that the cart is solid enough to support a larger piece of butcherblock. It's just a cheap Wayfair particleboard cart, and the current 'butcherblock' top is not very heavy.

Home Depot sells pine boards meant for shelves. They come in different widths and lengths. I’d buy one the right width, get them to cut it 25.75 long, stain and seal it and attach it to the top of the cart. If your cart is wider than the boards they sell, just put two, 12 inch boards together. They should butt up quite tight together. They aren’t very heavy as they are about an inch thick.

On the back, can you make a support for a folding leaf? That way it covers the gap but it doesn’t have to be sturdy like the front

Well, this is kind of “klugey”, but I’ve applied an adhesive door sweep at the back of a table or bookcase if I don’t want items to fall off the back. Kind of like the bit of trim at the back of the open shelf of your cart has. Maybe just add a bit of wood trim? Even something like a scrap of quarter-round? (I’m not that handy, though!)

Is the top easily removed? If so, replacing it with a deeper one would be good. In the meantime, I don't think it looks bad as is.

Since it is moveable, the area behind it would make a great place to store a folding stepstool or a couple of folding chairs, if you ever need extra seating for guests, or a way to get up to clean the tops of the cabinets or light fixtures.

@Joy Willis, great idea, except that at my height (5'1"), I need my stepladders to be waaaaay more accessible than that.

I would purchase a metal industrial 4 shelf rack for that space & move the cart in front of the window, put bamboo roll up blinds on the window...on the metal shelving I would buy a magnet strip to hold all utensils to be readily accessible for the butcher block!

There's a door there so it isn't really an option to put the cart in front of the window. But thanks for the suggestion. Also, I'm pretty sure the cabinets are IKEA, not Home Depot, but I can ask the landlord.

This may sound dumb, but I wonder if moving the toaster oven to the cart thereby having more counter space to the right would help alleviate the problem? (Hopefully cord is long enough.) Then you wouldn't need any modifications. I think it looks fine as is, changing hardware if desired as mentioned.

Maybe. We're hoping to get a KitchenAid Stand Mixer for that space though. :) (Ah, dreams...)

Buy a larger cart?

It looks like getting a wider (deeper) cart would put the top of the cart in front of the edge of the window. I'd stick with the cart you have and try moving stuff off of it to gain more usable depth.

Good suggestion from ljptwt7 to move the toaster oven and also the knives to the back of the cart. Then you wouldn't be dropping anything behind the cart and have a large open countertop next to it.

Thanks all! Some good suggestions here. A set of shelves with pot hooks behind the cart sounds like a winner of an idea. Now just to hunt down the right one for the space. Appreciate everyone's ideas!