The original recipe is South African, calling for Gem Squash. I've only seen seeds for gem squash available once in 8 years of looking, and I lost the packet in moving - the squash itself, I've never seen in stores. (Note, this is not "gem" watermelons, which are not only much larger, but melons.)
But hey, you're roasting a small squash and then stuffing it with blue cheese and sage leaves that have been crisped in butter. Acorn squash is close enough!
Original recipe here: https://realmealrevolution.com/recipes/sage-and-blue-cheese-roasted-squash
American translation as follows:
3-4 acorn squash
1 wedge stilton (5-8 oz)
1 handful sage leaves (call it a cup. These are seriously tasty, so more is better!)
1 stick butter
First, get out the cleaver and carefully whack the acorn squash in half. Scoop out all the seeds, then flop two halves cut-down on a plate and microwave for 5-7 minutes, until the shells are shiny and the squash beneath is soft when you poke the shell. (Use something not your finger to poke it. It's hot!)
Flip the squash halves cut-side-up on a cookie tray. Divide blue cheese and crumble into each hollow.
Meanwhile, melt the stick of butter on medium heat in a frying pan. When melted, add the sage leaves. Let the dish bubble to itself for a while - about the time the butter is turning sage-green and the milk solids are starting to turn dark brown, the sage leaves will look less fresh and more fried. Remove from heat, and spoon the butter and leaves over each squash. Try to get all the cut parts coated in butter, so they won't dry out.
Stick cookie tray in oven, turn on broiler to low, broil 5 minutes or so until the cheese is bubbly, lightly browned, and sage leaves crispy but not burnt. (If doing 4 squash, just use two trays and rotate them out.)
Serve with your main dish, and enjoy :-)