It’s an early summer afternoon in Madrid, and the world’s oldest restaurant is abuzz with a cacophony of tourist and local voices, knives and forks, bottles and glasses.

But just as the famed Restaurante Botín sees business returning to normal after the Spanish capital’s pandemic lockdowns, it has another challenge to overcome: soaring inflation. Retail prices in the Iberian nation surged 10.2% in June — a 37-year high and among the loftiest inflation rates in the euro area.

Economic…