I've never actually made the cheese variant myself, so I can't really recommend a recipe. I found this one though, and it's very from-scratch. I saw a few others that used store-bought cottage cheese but given that this recipe calls for mixing the flour in with the milk when making the cheese I'm not 100% sure that'd work out as well.

Ingredients

• 3½ litre (3500ml) milk
• 2½ decilitre all purpose wheat flour (210 gram)
• 1 tablespoon rennet
• 30 gram sweet almonds
• 4 bitter almonds
• 1½ decilitre whip cream (that's generally 40% fat here)
• 1 decilitre granulated sugar
• 3 eggs
• grease for the pan

My own notes:

1. It probably doesn't have to be specifically rennet, but if you use a different coagulant adapt the cheese-making portion of the recipe to match that.
2. I'd pour some of the milk into the flour, and mix that until you have a smooth batter, before pouring that mixture into the milk, rather than mixing the flour directly into the milk. Just to avoid lumps.
3. Speaking from experience making paneer, milk that's been pasteurised at a high temperature (I think usually referred to as ultra pasteurised) to extend its shelf-life is trickier to get to coagulate properly. I'd recommend avoiding that.

Directions:

Heat the milk to 37C (98.6F). Mix in the flour and add the rennet. Stir and let sit for approximately 30 minutes. Stir again so the whey separates out, and let sit for another 30 minutes.

Dampen a thin kitchen towel/cheese cloth and put in a colander. put the colander in a large bowl. Pour the cheese into the colander and let drain for approximately 8 hours in a refrigerator.

Turn the oven on 200C (392F).

Finely chop the sweet almonds. Grate the bitter almonds finely.

Put the cheese mixture in a bowl. Mix together cream, sugar, and egg in a separate bowl and combine the mixture together with the almonds with the cheese mixture. Grease a pan (2½ litres) and pour in the batter. Cook in the oven, preferably in a water bath, for approximately 55 minutes. Let the cake cool and set, you can do this in a refrigerator.

Serve the cheese cake lukewarm with whipped cream and jam.

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This looks to me like the Småland variation recipe. There's one from Hälsingland which I've never had. It sounds like it's quite different and it's generally served with cloudberries or a "juice sauce."

The wikipedia page for ostkaka also has this note, which I think was kind of fun.

According to the tradition from Småland, one always starts eating ostkaka from the middle. One theory for this is that in the old days, it was baked in a copper pot with a tin lining. If cracks appeared in the tin, the cheesecake would mix with the toxic copper. This way, the more distinguished guests would at least not ingest as much of the poison. Others claim it's because the cheesecake is creamiest in the middle and a bit drier and more burnt at the edges, which were saved for the children and the servants.