Add the oil to a small saucepan over medium heat. Once heated, add the shallots, cooking for two to three minutes, or until the shallots begin to soften.

Add the garlic, and chopped sundried tomatoes, cooking until fragrant.

Add the apple cider vinegar, honey, water, thyme, salt, and mustard seeds. Bring to a boil, cover, and reduce to a simmer for 25 minutes.

Remove the lid, and simmer for an additional 20 minutes, or until the liquid is reduced and it becomes a jammy consistency. Remove from heat, and let cool to room temperature.

Heat a skillet over medium-low heat.

Spread half a tablespoon of butter on each slice of challah. Place one piece of challah, buttered side down, in the skillet.

Spread the sun-dried tomato jam on one slice of toast, and layer with cheese. Top with the second slice, buttered side out.

Cook until the cheese begins to melt, and the challah turns golden brown, flipping once. I like to use a spatula to press the sandwich down slightly.

Once melted, remove from the skillet and slice.