Preheat the oven to 350 degrees.

Mix 2 tbsp of the olive oil and the garlic together in a small bowl.

Brush the portobello caps on both sides with the mixture, and sprinkle each side with salt and pepper.

Place them gill sides down on a baking sheet, and roast for 25 minutes.

When the mushrooms are cool enough to handle, slice each cap thinly at an angle, netting 8-10 slices per cap.

While the portobello caps are cooking, heat the remaining 1 tbsp olive oil in a pan over medium heat.

Add the onion and cook for about 5 minutes, until it begins to soften.

Turn the heat to low and cook the onion for 15-20 minutes, stirring occasionally.

If it begins to stick, deglaze the pan with some cooking sherry or water.

Cut the baguette into 4 equal portions 5-6 inches long, avoiding the rounded ends.

Slice each in half lengthwise.

Spread each of the 8 halves with 1 tbsp of the French Dip Spread.

Heat a large skillet over medium heat.

Place as many of the halves that will fit, spread-side down, for 3 minutes.

Repeat for all the halves.

Place 4 baguette bottom-halves, griddled side up, on a baking sheet lined with parchment paper.

Top each with ¼ of the sliced mushrooms and grilled onions.

Top with cheese.

Place in the 350 degree oven for about 10 minutes, until heated through and cheese melts.

Top with the remaining halves and bake for 3 minutes more.

Slice each sandwich in half at an angle and serve with ~⅓ cup of Mushroom Au Jus.