When using TypeScript interfaces (as recommended in the TypeScript tips page), mixin methods won't be recognized on the ILogLayer interface. Since it's difficult to extend ILogLayer directly (TypeScript doesn't allow extending interfaces from external modules in a way that captures mixin methods), you can create a composite type using an intersection type (&) that combines ILogLayer with the mixin interface:

import type { ILogLayer } from 'loglayer';
import type { IHotShotsMixin } from '@loglayer/mixin-hot-shots';

export type ILogLayerWithMixins = ILogLayer & IHotShotsMixin<ILogLayer>;

// Create your instance of LogLayer
const log: ILogLayerWithMixins = new LogLayer();

// Replace your usage of ILogLayer with ILogLayerWithMixins instead
function getLogger(): ILogLayerWithMixins {
  return log;
}