How to set up Email newsletters

So this is less a question on how to set up integration with sendgrid or mailchimp, and more along the lines of how would you go about creating an admin setup to create dynamic newsletters without having to write them thru code and push an update.

Specifically what im looking to do is send out newsletters about which recipes are trending, popular, in season, etc... So its not just a text based email but will need to toss in queries and css formatting. So far Ive figured out canned emails like welcome emails but not sure how to go about setting up a system where i can dynamically create emails in the admin section.