Preheat the oven to 200 °C.
Place your tart pan in the oven to warm up. After 5 minutes, pour in 70 grams of sugar. Swirl it around so it is evenly distributed, do not stir. Place it back in the oven. A caramel will form. Keep a close eye on it so the sugar doesn't burn. Occasionally swirl the pan. Caution: hot, hot, hot! (You can also melt the sugar in a pan over heat if you prefer.) Remove from the oven and let it cool completely.
Lower the oven temperature to 160 °C.
In a large bowl, whisk the eggs with the seeds from the vanilla pod, the instant coffee, and the remaining sugar. The goal is not to whip it too much; there should be as little foam as possible. Stir the milk and cream into the eggs.
Now place your pan with the set caramel into a larger pan, so you can cook it au bain-marie. Pour the egg-cream mixture into the pan, pour warm water between the two pans, and place in the oven.
Let it cook for 1 hour. The texture should still be a bit jiggly, but not liquid anymore.
Refrigerate overnight.
Loosen the edges, place a plate on top, and confidently flip it over. Tap the pan a bit if it doesn't come out immediately.
Tips
You can also prepare it without coffee. Then put a little more vanilla in it.