Pat the chicken thighs thoroughly dry with paper towels. Season generously with salt and pepper.

Heat the olive oil in a large skillet over medium high heat until shimmering. Sear the chicken thighs in batches until deeply golden brown on all sides, about 3-4 minutes per side. Do not crowd the pan. Remove chicken and set aside.

Add the sliced onion to the same skillet. Cook, stirring occasionally, until softened and lightly caramelized, about 5-7 minutes. Add the minced garlic and cook for 1 minute more until fragrant.

Deglaze the skillet with the white wine, scraping up any browned bits from the bottom of the pan. Let it simmer and reduce by half, about 3 minutes.

Transfer the seared chicken, caramelized onions, and deglazing liquid to your slow cooker. Add the chicken broth, 1 tablespoon of lemon juice, dried thyme, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Stir to combine.

Cover and cook on LOW for 3.5 to 4 hours, or until the chicken is fork tender and cooked through.

Once the chicken is cooked, remove it from the slow cooker and set aside on a plate. Keep warm.

In a medium bowl, whisk together the egg yolks and heavy cream until thoroughly combined and slightly lightened in color.

Stir in the chopped fresh dill and lemon zest into the egg yolk and cream mixture.

Carefully ladle about 1 cup of the hot cooking liquid from the slow cooker into the egg yolk mixture, whisking constantly. This tempering process prevents the yolks from scrambling.

Pour the tempered yolk mixture back into the slow cooker with the remaining cooking liquid. Stir gently to combine.

Turn the slow cooker to the WARM setting (or the lowest heat setting if your slow cooker has one) and cook, stirring occasionally, for about 10-15 minutes, or until the sauce has thickened slightly and coats the back of a spoon. **Crucially, do not let the sauce boil after adding the liaison, as this will cause it to curdle.**

Return the chicken thighs to the slow cooker and gently nestle them into the thickened sauce. Let them warm through for 5-10 minutes.

Taste the sauce and adjust seasoning with salt and pepper as needed. Add a touch more lemon juice if a brighter flavor is desired.

Serve the chicken thighs spooned over pasta, rice, or with crusty bread to soak up the exquisite sauce. Garnish with fresh dill sprigs, if desired.