Smoothing filled contours by interpolation

The following code creates and labels (including a colorbar) a figure showing filled contours for a 30 x 30 matrix called 'stab', made up of values between 0.0 and 2.1 in steps of 0.3.

I'm trying to figure out how to smooth the contours by interpolation: 30 steps in each dimension leads to pretty chunky contour lines.

Struggling to figure out how to create an interpolation grid and the relevant interpolation values.

Before asking a question like this I'd normally have at least had a go myself, but after reading every page and help file I can on this I just have no clue how to get started.

Any and all help gratefully received.

hold on;
colormap(winter);
cl = [0.0:0.3:2.1];
[C,h] = contourf(stab,cl);

axis xy;

% Relabel axes to fix scale
set(gca,'XTick',0:5:30)
set(gca,'XTickLabel',[0:.5:3.0])
set(gca,'YTick',0:5:30)
set(gca,'YTickLabel',[-1:.5:2])

% Label axes (could add units later)
xlabel ('q','Fontsize',16);
ylabel ('a','Fontsize',16);

% Label graph
title ('Stability Regions of Damped Matheiu Equation for b=0 to b=2.1','Fontsize',14);

hcb = colorbar;
set(hcb,'YTick',[0.0:0.3:2.1]);

hold off;