I started with this recipe and left out the bacon:
and I didn't have a red onion - so I used a yellow one
and I didn't have any plum tomatoes - so I used a can of diced tomatoes instead
I chopped the onion and cooled it in a little olive oil, then added the diced tomatoes and a little tomatoe paste from a tube. I let that cook down, as recommended, until it was pretty thick.
I cooked the pasta while the sauce was thickening up. Mixed the pasta with some grated Parmesan and the ricotta and stirred it all together, then added the pasta and mixed.