I am having a confuse about generics

example.ts

interface Z {
    potato: string
}

abstract class A<T> { // I want to indicate that T will always at least implement Z
    protected foo(bar: T) {
        console.log(bar.potato); // ERROR: [ts] Property 'potato' does not exist on type 'T'
    }
}

class B extends A<Z> {
    public bork() {
        const z: Z = {
            potato: 'tomato',
        }
        this.foo(z)
    }
}

const b = new B();

b.bork()

// Should output: 'potato'