Melt the butter with the canola oil in a large ovenproof casserole over high heat. Add the chicken thighs skin-side down and cook for 2–3 minutes per side until deeply golden. Don't rush this part — that color is flavor. Season generously with salt and pepper as they cook.

Scatter the sliced portobello mushrooms over and around the chicken. Sprinkle the herb blend and garlic evenly across everything. The kitchen should smell incredible at this point. If it doesn't, add more thyme.

Pour in the chicken stock and wine. Bring to a boil, then cover and reduce the heat to medium-low. It needs a slow, steady simmer — about 25–30 minutes. This braise will develop into a gorgeous herb-scented broth. You'll want to devour it now, but it needs to cook the chicken through to a temp of 185–190°F. There's nothing worse than cutting into a juicy thigh and seeing it's still raw at the bone. Now is a great time to pour your own glass of wine and start mental gymnastics with puff pastry — skip to below. See you back here for Step 4 of the sauce in a bit.

Lift the chicken thighs and mushrooms out of the pan and set aside. Bring the braising liquid to a boil and let it reduce by about half — it should thicken and concentrate into a deep savory sauce. This may take as little as 15 to as much as 30 minutes to reduce fully. It's hard to over-reduce.

Stir the heavy cream or crème fraîche into the reduced sauce. Let it come together over low heat into a smooth, silky finish. Taste and adjust salt and pepper. It should be tangy, bright, herbaceous, and a bit briny as well.

Return the chicken and mushrooms to the pan, turning them to coat well in the sauce. Serve directly from the casserole — this is that kind of dish. Tuck a few fresh thyme sprigs in for the table.

Follow package instructions for thawing and unfolding. Most store-bought puff pastry folds into thirds — those fold lines are your first set of cut guides.

Slice the sheet into 3 long strips along the fold lines. For each strip, mark the midpoint of one long edge, then cut diagonally from each of the two near corners down to that midpoint. You'll get 3 triangles per strip — 9 total. See the diagram above.

Crimp all edges of each triangle with a fork — this helps them puff and hold their shape. Brush lightly all over with the beaten egg.

Bake on a sheet pan per package instructions — usually 10–12 minutes at 375°F — until puffed and deep golden. Watch the edges; they can color fast.

Straight from the oven, smear each triangle generously with garlic compound butter. Nestle 1–2 triangles into each chicken bowl at the table.

Stir the buttermilk into the heavy cream in a pint Mason jar. Loosely cover — not airtight — and leave at room temperature until thickened. Start checking at 12 hours; it may take up to 48 depending on your kitchen temperature and the cream you used.