After cooking steak. Let skillet cool about 5 minutes. While skillet is cooling, peel and finely chop 1 shallot. Smash 2 garlic cloves with the flat side of your knife and remove peel. Cut ¼ cup (½ stick) butter into 4 Tbsp.-size pieces. Set aside and have at the ready.

Using paper towels, blot around skillet to soak up any blackened oil, but leave browned stuck-on bits behind.

Place skillet back over medium-low heat and add shallot, garlic, 2 sprigs thyme, and 2 Tbsp. butter. Swirl skillet to melt butter and cook, stirring often with a whisk, until shallot is golden brown, 2–3 minutes.

Add ½ cup water to skillet and whisk to dissolve stuck-on bits. Whisk in 2 Tbsp. mustard and 2 tsp. Worcestershire sauce until smooth.

Still working over medium-low heat, add remaining 2 Tbsp. butter and whisk constantly until butter is dissolved and sauce is smooth and thick, about 1 minute. Remove skillet from heat. Taste sauce and season with more salt (only if needed) and pepper.

Cut steak against the grain into ½”-thick slices and arrange on a platter.

Spoon pan sauce over steak and serve.