Yml variables error

GitLab CI/CD
1

Here is my .yml:

variables:
    NUGET_PATH: "C://Tools//Nuget//nuget.exe"
    MSBUILD_PATH: "C://Program Files (x86)//Microsoft Visual Studio//2019 BuildTools//MSBuild//Current//Bin//msbuild.exe"

stages:
  - build

build:
  stage: build
  tags:
    - dotnet
  script:
    - $NUGET_PATH restore
    - $MSBUILD_PATH /p:Configuration=Release /p:DeployOnBuild=true /clp:ErrorsOnly

Error:
$ $NUGET_PATH restore
'$NUGET_PATH' is not recognized as an internal or external command, operable program or batch file.

Girlab version: GitLab Enterprise Edition [12.0.3-ee]

What am I doing wrong?