Just to add on top of the quality reference provided by srean, I like to first drill in Bayesian principles and then use this article to derive PAC-Bayes from that: https://arxiv.org/abs/1605.08636
Regular PAC falls out by taking a uniform prior over a finite hypothesis class (and then building up VC dimension if desired, but usually by this point you realise why the bounds are unlikely to be good).
Seems I was misremembering the dates. The Langford and Banerjee papers/turorials I had in mind were
On Bayesian Bounds https://dl.acm.org/doi/10.1145/1143844.1143855
Tutorial on Practical Prediction Theory for Classification https://jmlr.csail.mit.edu/papers/v6/langford05a.html
The first one is quite in the same spirit that you like.