Preheat your oven to 350°F (177°C) and get your large or mini tart cases ready.  Mine are non-stick, so don't need greased.

Crust: Mix the melted butter, sugar, vanilla extract, and salt together in a medium bowl.

Add the flour and rosemary and stir to completely combine. The dough will be a little greasy and very thick.

Using a rubber spatula or your hands, press dough firmly into your tart pans, making sure it's even on the bottom and around the sides (fairly thin is preferable, as it puffs while baking).

Bake for 15 minutes or until the edges are very lightly browned. Remove from the oven.

Using a fork, poke a few holes all over the top of the warm crust (not all the way through the crust). This helps the filling stick.

Filling: Whisk all of the filling ingredients EXCEPT the jam together until combined. Pour into the warm tart crusts.

Take small spoonfuls of jam and drop them over the top of the filling, then use a toothpick, skewer, or knife to gently swirl the sauce and filling together.  I would put the tiniest flake of sea salt on top as well.

Bake for 12-20 minutes (depending on whether it's a mini or regular size tart), just until the center of the tart no longer jiggles when you give the pan a light tap. It will still be sticky on top. Avoid over-baking because the tart will taste rubbery.  In fact, err on the side of under-baking because the filling also has a chance to set up in the refrigerator. You want a creamy soft filling.)

Remove the tarts from the oven and place on a cooling rack. Cool completely at room temperature, then chill in the refrigerator uncovered for at least 2 hours and up to 1 day. If chilling for longer than 2 hours, cover them.

Remove the sides of the tart pan (if loose-bottomed) and serve.  Cover leftovers tightly and refrigerate for up to 1 week.