The archetypes are defined in the archetypes folder, for both post and portfolio.

The archetypes are defined in YAML, so Front matter is formatted in YAML too. You can easily change them to TOML in your own archetypes is you wish to.

For example:

---
title: title
description: desc
date: "2019-05-02T19:47:09+02:00"
---

to

+++
title = "title"
description: "desc"
date: "2019-05-02T19:47:09+02:00"
+++