Step 1

In a small bowl, soak porcini in the boiling water until soft, about 20 minutes. Working over the bowl, lift out porcini, and squeeze out liquid. Coarsely chop porcini. Pour liquid through a fine sieve into another bowl, and reserve.

Step 2

Cook bacon in a large skillet over medium heat until crisp, about 5 minutes per side. Drain on paper towels. Pour off rendered bacon fat, reserving 1/4 cup. Wipe skillet clean. Coarsely chop bacon.

Step 3

Return 3 tablespoons bacon fat to skillet. Add leek and garlic; cook over medium heat, stirring occasionally, until translucent, about 2 minutes. Add fresh mushrooms and porcini, then the salt and pepper. Raise heat to high; cook, stirring, until mushrooms are tender, 5 to 8 minutes. Add thyme; cook 2 minutes more. Transfer to a plate; let cool.

Step 4

With an electric mixer, whisk cream cheese in a medium bowl until smooth. Gradually add sour cream; whisk until smooth. By hand, stir in mushrooms, three-quarters of the bacon, scallions, and 2 tablespoons porcini liquid. If necessary, add more porcini liquid to reach desired consistency.

Step 5

Garnish dip with scallions and remaining bacon. If desired, cook sliced mushrooms in remaining tablespoon bacon fat in a medium skillet over medium heat, stirring occasionally, until golden brown, about 2 minutes. Scatter over dip. Serve with waffle chips if desired.